Zinc-based plated steel sheet

ABSTRACT

[Object] To provide a zinc-based plated steel sheet excellent in coating film adhesiveness after hot pressing more conveniently. 
     [Solution] A zinc-based plated steel sheet according to the present invention comprises: a zinc-based plated steel sheet that is a base metal; and a surface treatment layer formed on at least one surface of the zinc-based plated steel sheet, in which the surface treatment layer contains one or more oxides selected from titanium oxide, nickel oxide, and tin(IV) oxide each having a particle size of more than or equal to 2 nm and less than or equal to 500 nm, in a range of more than or equal to 0.2 g/m 2  and less than or equal to 2 g/m 2  per one surface.

TECHNICAL FIELD

The present invention relates to a zinc-based plated steel sheet.

BACKGROUND ART

These days, to protect the environment and prevent global warming, thesuppression of the consumption of fossil fuel is increasingly demanded,and the demand influences various manufacturing industries. For example,automobiles, which are indispensable to daily life and activity as amoving means, are no exception, and improvements in fuel efficiency etc.by the weight reduction of car bodies etc. are required. However, forautomobiles, simply achieving a weight reduction of the car body is notpermitted in terms of the functionality of the product, and it isnecessary to ensure proper safety.

Most of the structure of the automobile is formed of iron-basedmaterials, in particular steel sheets, and the reduction in the weightof the steel sheet is important to the weight reduction of the car body.However, as described above, simply reducing the weight of the steelsheet is not permitted, and ensuring the mechanical strength of thesteel sheet is required at the same time. Such a demand on the steelsheet is placed not only in the automobile manufacturing industry butalso in various manufacturing industries similarly. Hence, research anddevelopment are being made to enhance the mechanical strength of thesteel sheet and thereby obtain a steel sheet in which the mechanicalstrength can be maintained or improved even when the wall thickness ismade smaller than those of conventionally used steel sheets.

In general, a material having high mechanical strength tends to decreasein shape fixability in molding such as bending, and is difficult to moldinto a complicated shape. As a means for solving such a problem withmoldability, what is called “the hot pressing method (also called thehot stamping method or the die quenching method)” is given. In the hotpressing method, a material to be molded is once heated to hightemperature, the steel sheet softened by heating is pressed to bemolded, and then cooling is performed. By the hot pressing method, thematerial of the object can be easily pressed because the material isonce heated to high temperature and softened. Furthermore, themechanical strength of the material can be enhanced by the quenchingeffect by the cooling after molding. Thus, a molded product in whichboth good shape fixability and high mechanical strength are achieved canbe obtained by the hot pressing method.

However, when the hot pressing method is used for a steel sheet, thesurface of the steel sheet is oxidized by the steel sheet being heatedto a high temperature of 800° C. or more, and scales (compounds) areproduced. Hence, the process of removing the scales (what is called adescaling process) is needed after hot pressing is performed, andproductivity is reduced. In addition, in a member etc. requiringcorrosion resistance, it is necessary to perform anti-rust treatment ormetal covering on the surface of the member after processing, and asurface cleaning process and a surface treatment process are needed;consequently, productivity is further reduced.

As a method to suppress such a reduction in productivity, for example, amethod in which a steel sheet to be hot pressed is provided with acovering in advance is given. Various materials such as organic-basedmaterials and inorganic-based materials are generally used as thecovering on the steel sheet. Among these, plated steel sheets based onzinc (Zn), which has a sacrificial anti-corrosion action on the steelsheet, are widely used as automotive steel sheets etc. from theviewpoints of the anti-corrosion capacity and the steel sheet productiontechnique.

By providing a Zn-based metal covering, the production of scales on thesurface of the steel sheet can be prevented, and processes such asdescaling become unnecessary; thus, the productivity of molded productsis improved. In addition, the Zn-based metal covering has also ananti-rust effect, and therefore also corrosion resistance is improved.Patent Literature 1 to Patent Literature 4 below disclose a method ofhot pressing a plated steel sheet that is obtained by providing aZn-based metal covering to a steel sheet having a prescribed componentcomposition.

In Patent Literature 1 to Patent Literature 3 below, a hot-dipgalvanized steel sheet or an alloyed hot-dip galvanized steel sheet isused as a steel sheet for hot pressing. By using a hot-dip galvanizedsteel sheet or an alloyed hot-dip galvanized steel sheet for hotpressing, a structure member can be molded without iron oxides (that is,scales) being formed on the surface. Further, in view of the fact that,when a Zn oxide layer is formed thick on the surface of a heat-treatedsteel material obtained by hot pressing a Zn-based plated steel sheet,the coating film adhesiveness and the post-coating corrosion resistanceof the heat-treated steel material are adversely affected, PatentLiterature 4 below discloses an invention in which a heat-treated steelmaterial is subjected to shot blasting to remove a Zn oxide layer or issubjected to coating after the thickness of a Zn oxide layer is reduced.

Patent Literature 5 and Patent Literature 6 below disclose inventionsthat improve the coating film adhesiveness and the post-coatingcorrosion resistance of a heat-treated steel material obtained by hotpressing a Zn-based plated steel sheet. Patent Literature 5 belowdiscloses an invention in which a hot-dip galvanized steel sheet withits surface covered with a silicone resin coating film is used as asteel sheet for hot pressing, and Patent Literature 6 below discloses aninvention in which a hot-dip galvanized steel sheet covered with abarrier layer containing phosphorus (P) and silicon (Si) (a phosphate isgiven as an example of P, and colloidal silica is given as an example ofSi) is used as a steel sheet for hot pressing.

Patent Literature 7 below discloses a technology in which elements thatare easier to oxidize than Zn (easily oxidizable elements) are addedinto a galvanized layer and an oxide layer of these easily oxidizableelements is formed on the outer layer of the galvanized layer during thetemperature increase in hot pressing, and thereby the volatilization ofZn is prevented.

According to the inventions disclosed by Patent Literature 5 to PatentLiterature 7 below, since a galvanized layer is covered with the barrierlayer described above, the vaporization of Zn is suppressed, and thusthe adhesiveness of an intermediate coating film and an over-coatingfilm and post-coating corrosion resistance are good.

CITATION LIST Patent Literature

Patent Literature 1: JP 2003-73774A

Patent Literature 2: JP 2003-129209A

Patent Literature 3: JP 2003-126921A

Patent Literature 4: JP 2004-323897A

Patent Literature 5: JP 2007-63578A

Patent Literature 6: JP 2007-291508A

Patent Literature 7: JP 2004-270029A

SUMMARY OF INVENTION Technical Problem

However, there may be a case where satisfactory post-coatingadhesiveness is not obtained in the following cases: the Zn-based platedsteel sheet is hot pressed; and the attached amount of a phosphatecoating film formed through phosphate treatment and a treatment coatingfilm (FF treatment coating film) obtained by using an aqueous solutioncontaining Zr ions and/or Ti ions and fluorine, and containing 100 to1000 ppm of free fluoride ions (hereinafter, referred to as FF chemicalconversion treatment liquid).

In general, in the case where chemical conversion treatability is notsufficient (for example, in the case where attachment unevenness, lackof hiding, and the like occur), the adhesiveness between the steel sheetand an electrodeposition coating film is not sufficiently secured, andas a result, post-coating adhesiveness becomes poor. Reasons why thechemical conversion treatability becomes insufficient include thatdegreasing and surface conditioning before the chemical conversiontreatment are insufficient, and that the concentration and thetemperature of the chemical conversion treatment liquid and the time ofthe chemical conversion treatment are insufficient.

As another reason, there is given that the chemical convertibility isreduced due to Al contained in hot-dip galvanizing. Specifically, the Alin the hot-dip galvanizing layer diffuses and moves to the outer layerof the plating layer not only during the formation of a plating coatingfilm but also during the heating of hot pressing, and forms an Al oxidefilm. Since the Al oxide film does not dissolve in phosphoric acid, thereaction between Zn and a phosphate (for example, zinc phosphate) isinhibited, and a phosphate coating film is less likely to be formed inthe area where the Al oxide film is formed. Consequently, phosphatetreatability is low in the area where the Al oxide film is formed. Inparticular, phosphate treatability is significantly reduced in the casewhere, in the hot pressing process, the steel sheet is rapidly heated tothe Ac₃ point or more by energization heating or induction heating andthen press molding is quickly performed, and as a result, coatingadhesiveness is also reduced.

In addition, when the present inventors conducted a check experiment ona heat-treated steel material disclosed by Patent Literature 5 abovethat was obtained by using, as a steel sheet for hot pressing, a hot-dipgalvanized steel sheet with its surface covered with a silicone resincoating film, it has been found that, as will be described later,although post-coating corrosion resistance in a cycle corrosion test inwhich a dry and a wet environment are repeated is good, coatingadhesiveness is not always good. Hence, a heat-treated steel materialobtained by the invention disclosed in Patent Literature 5 above is notsuitable for use as it is for a part or a member in which water islikely to collect because of the structure (for example, a bag-likestructural part below the door, a member with a closed cross section inthe engine compartment, etc.), for example.

On the other hand, the addition of easily oxidizable elements into azinc plating layer disclosed in Patent Literature 7 above requires newoperational actions, such as the temperature control of the plating bathand dross measures.

Thus, the present invention has been made in view of the issue mentionedabove, and an object of the present invention is to provide a zinc-basedplated steel sheet excellent in coating film adhesiveness after hotpressing more conveniently.

Solution to Problem

On the basis of the findings obtained by extensive studies on the platedsteel sheet for hot pressing of the object mentioned above, the presentinventors have thought up the following zinc-based plated steel sheet.

The gist of the present invention is as follows.

-   (1)

A zinc-based plated steel sheet comprising:

a zinc-based plated steel sheet that is a base metal; and

a surface treatment layer formed on at least one surface of thezinc-based plated steel sheet, in which

the surface treatment layer contains one or more oxides selected fromtitanium oxide, nickel oxide, and tin(IV) oxide each having a particlesize of more than or equal to 2 nm and less than or equal to 100 nm, ina range of more than or equal to 0.2 g/m² and less than or equal to 2g/m² per one surface.

-   (2)

The zinc-based plated steel sheet according to (1), in which

the surface treatment layer further contains at least one of one or morephosphorus-containing compounds, one or more vanadium-containingcompounds, one or more copper-containing compounds, one or morealuminum-containing compounds, one or more silicon-containing compounds,or one or more chromium-containing compounds in the following range as acontent per one surface,

the one or more phosphorus-containing compounds: more than or equal to0.0 g/m² and less than or equal to 0.01 g/m² on a P basis,

the one or more vanadium-containing compounds: more than or equal to 0.0g/m² and less than or equal to 0.01 g/m² on a V basis,

the one or more copper-containing compounds: more than or equal to 0.0g/m² and less than or equal to 0.02 g/m² on a Cu basis,

the one or more aluminum-containing compounds: more than or equal to 0.0g/m² and less than or equal to 0.005 g/m² on an Al basis,

the one or more silicon-containing compounds: more than or equal to 0.0g/m² and less than or equal to 0.005 g/m² on a Si basis, and

the one or more chromium-containing compounds: more than or equal to 0.0g/m² and less than or equal to 0.01 g/m² on a Cr basis.

-   (3)

The zinc-based plated steel sheet according to (1) or (2), in which

the particle size of each of the one or more oxides selected fromtitanium oxide, nickel oxide, and tin(IV) oxide is more than or equal to5 nm and less than or equal to 50 nm.

-   (4)

The zinc-based plated steel sheet according to any one of (1) to (3), inwhich

the content of the one or more oxides selected from titanium oxide,nickel oxide, and tin(IV) oxide is more than or equal to 0.4 g/m² andless than or equal to 1.5 g/m² per one surface.

-   (5)

The zinc-based plated steel sheet according to any one of (1) to (4), inwhich

the one or more oxides are titanium oxide.

-   (6)

The zinc-based plated steel sheet according to any one of (1) to (5), inwhich

the zinc-based plated steel sheet is a zinc-based plated steel sheet forhot pressing.

Advantageous Effects of Invention

As described above, according to the present invention, even though thechemical conversion treatment is insufficient, it becomes possible toimprove the coating adhesiveness to a coating film provided after hotpressing.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present invention aredescribed in detail.

<1. Zinc-Based Plated Steel Sheet>

A Zn-based plated steel sheet according to an embodiment of the presentinvention includes a Zn-based plating layer on a ground steel sheet, andfurther includes a surface treatment layer described in detail below onat least one surface of the hot-dip Zn-based plating layer. The surfacetreatment layer includes a coating layer containing one or more oxidesselected from titanium oxide, nickel oxide, and tin(IV) oxide eachhaving a particle size of more than or equal to 2 nm and less than orequal to 100 nm, in the range of more than or equal to 0.2 g/m² and lessthan or equal to 2 g/m² per one surface as an attached amount. TheZn-based plated steel sheet having such a configuration can be suitablyused for the hot pressing method described above. Hereinafter, theconfiguration of the Zn-based plated steel sheet will be described indetail.

(1) Ground Steel Sheet

The ground steel sheet used for the Zn-based plated steel sheetaccording to the present embodiment is not particularly limited, andvarious steel sheets having known characteristics and chemicalcompositions may be used. The chemical composition of the steel sheet isnot particularly limited, but is preferably a chemical composition withwhich high strength is obtained by quenching. For example, when it isattempted to obtain a heat-treated steel material with a tensilestrength of 980 MPa or more, an example of the ground steel sheet ismade of steel for quenching having a chemical composition of, in mass %,C: 0.05 to 0.4%, Si: less than or equal to 0.5%, Mn: 0.5 to 2.5%, P:less than or equal to 0.03%, S: less than or equal to 0.01%, sol. Al:less than or equal to 0.1%, N: less than or equal to 0.01%, B: 0 to0.005%, Ti: 0 to 0.1%, Cr: 0 to 0.5%, Nb: 0 to 0.1%, Ni: 0 to 1.0%, Mo:0 to 0.5%, and the balance: Fe and impurities.

When it is attempted to obtain a heat-treated steel material with arelatively low strength in which the strength becomes less than 980 MPaduring quenching, the chemical composition of the ground steel sheet isnot necessarily be in the range described above.

The total amount of Mn and Cr contained is preferably 0.5 to 3.0% fromthe viewpoint of quenchability during the quenching described above andthe viewpoint of forming Mn oxides and Cr oxides contained in a zincoxide layer after heating. The total amount of Mn and Cr contained ismore preferably 0.7 to 2.5%.

When Mn and Cr are contained as the chemical composition of the steelsheet, part of the zinc oxide layer formed on the outer layer after hotpressing becomes composite oxides containing Mn and Cr. Coatingadhesiveness after phosphate-based chemical conversion treatment isfurther improved by these composite oxides containing Mn and Cr beingformed. Although details are unknown, it is presumed that, by thesecomposite oxides being formed, the alkali resistance of thephosphate-based chemical conversion treatment coating film formed isimproved as compared to zinc oxide, and good coating adhesiveness isexhibited.

In the case where Mn and Cr are contained as the chemical composition ofthe steel sheet, the content of Mn and Cr is preferably in the range of,in mass %, more than or equal to 0.5% and less than or equal to 3.0%,and more preferably in the range of, in mass %, more than or equal to0.7% and less than or equal to 2.5%. In the case where the content ofMn+Cr is less than 0.5%, zinc oxide that is formed on the outer layerafter hot pressing and composite oxides that contain Mn and Cr areinsufficient, and it may be difficult to bring out more satisfactorycoating adhesiveness. On the other hand, in the case where the contentof Mn+Cr exceeds 3.0%, although there is no problem with coatingadhesiveness, the cost is increased, and furthermore the toughness ofthe spot welded portion may be significantly reduced and the wettabilityof plating may be significantly degraded.

(2) Zn-Based Plating Layer

The Zn-based plating layer according to the present embodiment is notparticularly limited, and commonly known zinc-based plating may be used.Specifically, examples of the Zn-based plating layer according to thepresent embodiment include hot-dip galvanizing, alloyed hot-dipgalvanizing, hot-dip Zn-55% Al-1.6% Si plating, hot-dip Zn-11% Alplating, hot-dip Zn-11% Al-3% Mg plating, hot-dip Zn-6% Al-3% Mgplating, hot-dip Zn-11% Al-3% Mg-0.2% Si plating, Zn electroplating,Zn—Ni electroplating, and Zn—Co electroplating. It is also effective toform a covering of plating of the components mentioned above by a methodsuch as vapor deposition; thus, the method of plating is notparticularly limited.

In the present embodiment, as a specific hot-dip plating operation, anoperation in which a steel sheet is dipped in a plating bath in which Znor a Zn alloy in a molten state is retained and the steel sheet ispulled up from the plating bath is performed. The amount of platingattached to the steel sheet is controlled by adjusting the speed of thepulling-up of the steel sheet, the flow rate and the flow velocity ofwiping gas jetted from a wiping nozzle provided above the plating bath,etc. Alloying treatment is performed by, after plating treatment likethe above, additionally heating the plated steel sheet using a gasfurnace or an induction heating furnace, a heating furnace in whichthese are combined, or the like. The plating operation may also beperformed by the method of continuously plating a coil or the method ofplating a cut sheet single body.

In the present embodiment, as a specific plating operation in the caseof using electroplating, electrolysis treatment is performed in anelectrolyte solution containing Zn ions, using the steel sheet, as anegative electrode, and a counter electrode. The amount of platingattached to the steel sheet is controlled by the composition of theelectrolyte solution, the current density, and the electrolysis time.

The thickness of the Zn-based plating layer (that is, the amount of theZn-based plating layer attached) is preferably in the range of 20 g/m²to 100 g/m² per one surface. In the case where the thickness of theZn-based plating layer is less than 20 g/m² per one surface, theeffective amount of Zn after hot pressing cannot be ensured andcorrosion resistance is insufficient; thus, this is not preferable. Inthe case where the thickness of the Zn-based plating layer is more than100 g/m² per one surface, the processability and the adhesiveness of theZn-based plating layer are reduced; thus, this is not preferable. A morepreferred thickness of the Zn-based plating layer is in the range of 30g/m² to 90 g/m² per one surface.

(3) Surface Treatment Layer

On the Zn-based plating layer, there is further formed a surfacetreatment layer containing one or more oxides selected from titaniumoxide, nickel oxide, and tin(IV) oxide.

Here, the “one or more oxides selected from titanium oxide, nickeloxide, and tin(IV) oxide” represents, taking titanium oxide as anexample, a substance that contains oxide of titanium (Ti) as a maincomponent, which exists in a state of being dispersed in a treatmentliquid as a solid having a size of several nanometers or more as aprimary particle size, and does not exist in a state of being dissolvedin the treatment liquid like titanium chelate. Also in the same manner,nickel oxide and tin(IV) oxide represent a substance that contains oxideof nickel (Ni) as a main component and a substance that contains oxideof tin (Sn) as a main component, respectively, which each exist in astate of being dispersed in a treatment liquid as a solid having a sizeof several nanometers or more as a primary particle size, and do notexist in a state of being dissolved in the treatment liquid. Using theone or more oxides selected from titanium oxide, nickel oxide, andtin(IV) oxide being dispersed in a treatment liquid as a solid, itbecomes possible to provide a heat-treated steel material excellent indurability even in an environment of dipping in salt water. Note thatthe one or more oxides selected from titanium oxide, nickel oxide, andtin(IV) oxide exist in a state of particles in the surface treatmentlayer.

To be specific, the one or more oxides selected from titanium oxide,nickel oxide, and tin(IV) oxide each have a particle size (primaryparticle size) of more than or equal to 2 nm and less than or equal to100 nm. For the particle size of the one or more oxides selected fromtitanium oxide, nickel oxide, and tin(IV) oxide, a smaller size isadvantageous in terms of post-coating corrosion resistance, but thosewith a particle size of less than 2 nm are difficult to obtain and aredisadvantageous in terms of cost. Further, in the case where theparticle size of the one or more oxides selected from titanium oxide,nickel oxide, and tin(IV) oxide exceeds 100 nm, an influence given tothe steel sheet by the titanium oxide particle decreases during heatingin hot pressing (because a contact area with the plated steel sheet issmall); thus, this is not preferable.

In addition, among these oxides, titanium oxide not only has the featurementioned above but also can suppress excessive oxidation andvaporization of Zn during hot pressing, and can enhance not only coatingfilm adhesiveness after hot pressing but also corrosion resistance afterhot pressing. It is surmised that titanium oxide usually exists in astate of a metal oxide stably, but reacts with zinc oxide formed duringheating in hot pressing and forms a composite oxide with zinc oxide, andthereby suppresses excessive oxidation and vaporization of Zn. To obtainthis effect more efficiently, the particle size of titanium oxidementioned above is preferably more than or equal to 2 nm and less thanor equal to 100 nm.

The particle size of the one or more oxides selected from titaniumoxide, nickel oxide, and tin(IV) oxide is preferably more than or equalto 5 nm and less than or equal to 50 nm.

The particle size (primary particle size) of the one or more oxidesselected from titanium oxide, nickel oxide, and tin(IV) oxide can bemeasured by a known method; for example, the measurement can be made bya method in which a cross section-embedded sample is prepared aftercoating, several particle sizes of the one or more oxides selected fromtitanium oxide, nickel oxide, and tin(IV) oxide in the coating film aremeasured, and the average of the obtained measurement results is takenas the particle size.

The surface treatment layer included in the Zn-based plated steel sheetaccording to the present embodiment contains the one or more oxidesselected from titanium oxide, nickel oxide, and tin(IV) oxide in therange of more than or equal to 0.2 g/m² and less than or equal to 2 g/m²per one surface. When the content of the one or more oxides selectedfrom titanium oxide, nickel oxide, and tin(IV) oxide in the surfacetreatment layer is in the range of more than or equal to 0.2 g/m² andless than or equal to 2 g/m² per one surface, satisfactory adhesivenessbetween the surface of the steel sheet and an electrodeposition coatingfilm is exhibited even in the case where the attached amount of varioustypes of chemical conversion treatment (for example, phosphate treatmentor FF chemical conversion treatment) performed on the Zn-based platedsteel sheet is not sufficient. Although a detailed mechanism is notclear, the one or more oxides selected from titanium oxide, nickeloxide, and tin(IV) oxide are present on the surface of the steel sheetafter heat treatment; thereby, some influence is given to the cohesiondeposition of the electrodeposition coating film duringelectrodeposition coating, and the oxides and the electrodepositioncoating film adhere strongly; thus, it is presumed that strongadhesiveness can be exhibited even when chemical conversion treatment(phosphate treatment or FF chemical conversion treatment) is notsufficient.

In the case where the content of the one or more oxides selected fromtitanium oxide, nickel oxide, and tin(IV) oxide in the surface treatmentlayer is less than 0.2 g/m² per one surface, the one or more oxidesselected from titanium oxide, nickel oxide, and tin(IV) oxide after hotpressing are not sufficiently present, and hence, coating adhesivenessafter hot pressing cannot be ensured sufficiently. On the other hand, inthe case where the content of the one or more oxides selected fromtitanium oxide, nickel oxide, and tin(IV) oxide in the surface treatmentlayer exceeds 2 g/m² per one surface, the cost of the Zn-based platedsteel sheet according to the present embodiment is increased, and it ispresumed that the cohesive force of the surface treatment layer isweakened and a coating film that is formed on the surface treatmentlayer after hot pressing is likely to peel off.

In addition, in the case where the content of the titanium oxide is lessthan 0.2 g/m² per one surface, a sufficient amount of a composite oxidewith zinc oxide cannot be formed, and the oxidation and vaporization ofZn cannot be efficiently suppressed.

The content of the one or more oxides selected from titanium oxide,nickel oxide, and tin(IV) oxide in the surface treatment layer ispreferably more than or equal to 0.4 g/m² and less than or equal to 1.5g/m² per one surface.

Specific examples of the one or more oxides selected from titaniumoxide, nickel oxide, and tin(IV) oxide are shown below.

Specific example of commercially available products of titania solincludes TKS (registered trademark) series manufactured by TaycaCorporation.

Example of nickel oxide includes nickel oxide particles of commerciallyavailable (nano)powder.

Typical example of tin(IV) oxide includes tin(IV) oxide sol that is atreatment liquid containing tin(IV) oxide, and specific example ofcommercially available products includes Ceramace manufactured by TakiChemical Co., Ltd.

In forming the surface treatment layer, the treatment liquid or the likein which the one or more oxides selected from titanium oxide, nickeloxide, and tin(IV) oxide are dispersed may be applied as it is to theZn-based plated steel sheet, however, in order to improve stability ofthe treatment liquid and adhesiveness of the surface treatment layer, itis more preferred that the treatment liquid have a resin or acrosslinking agent mixed therein, and the treatment liquid be applied tothe Zn-based plated steel sheet.

In the case where the above sol in which the one or more oxides selectedfrom titanium oxide, nickel oxide, and tin(IV) oxide are dispersed isused, a water-soluble or water-dispersible resin is preferably used asthe resin. Examples of the resin include a polyurethane resin, apolyester resin, an epoxy resin, a (meth)acrylic resin, a polyolefinresin, a phenol resin, and modified products of those resins. In thecase where zirconia powder is used, a solvent resin in which any ofvarious solvents is used as the solvent may be used in addition to theabove-mentioned water-based resin.

Examples of the crosslinking agent include a zirconium carbonatecompound, an organic titanium compound, an oxazoline polymer, awater-soluble epoxy compound, a water-soluble melamine resin, awater-dispersible blocked isocyanate, and a water-based aziridinecompound.

Further, examples of the other component that is preferably furthercontained in the surface treatment layer according to the presentembodiment include one or more selected from zirconia, lanthanum oxide,cerium oxide, and neodymium oxide.

When zirconia, lanthanum oxide, cerium oxide, or neodymium oxidementioned above is contained in the surface treatment layer, duringheating, zirconia, lanthanum oxide, cerium oxide, or neodymium oxide inthe surface treatment layer makes harmless an Al oxide that is presentbefore hot pressing and is formed during hot pressing. Thereby, theformation of zinc oxide during hot pressing is accelerated; thus,phosphate treatability after hot pressing is enhanced, and coating filmadhesiveness is improved. Although details of the fact that an Al oxideis made harmless during heating by zirconia, lanthanum oxide, ceriumoxide, or neodymium oxide are unknown, it is presumed that zirconia,lanthanum oxide, cerium oxide, or neodymium oxide dissolves an Al oxideformed on the surface of the steel sheet, thereby Zn, which isrelatively easy to oxide after Al, is oxidized during hot pressing, andconsequently the production of zinc oxide (ZnO), which is excellent inchemical convertibility, is accelerated. To obtain this effect moreefficiently, the particle size of the oxide mentioned above ispreferably more than or equal to 5 nm and less than or equal to 500 nm.

The amount of the one or more selected from zirconia, lanthanum oxide,cerium oxide, and neodymium oxide contained in the surface treatmentlayer is preferably in the range of more than or equal to 0.2 g/m² andless than or equal to 2 g/m² per one surface. When the amount of the oneor more selected from zirconia, lanthanum oxide, cerium oxide, andneodymium oxide contained in the surface treatment layer is less than0.2 g/m² per one surface, sufficient zirconia, lanthanum oxide, ceriumoxide, and neodymium oxide are not present after hot pressing;consequently, the effect of making harmless an Al oxide of the platedsurface is reduced, and it may be difficult to sufficiently ensurecoating adhesiveness after hot pressing. On the other hand, when theamount of zirconia etc. contained in the surface treatment layer is morethan 2 g/m² per one surface, the cost of the Zn-based plated steel sheetaccording to the present embodiment is increased, and it is presumedthat the cohesive force of the surface treatment layer is weakened and acoating film that is formed on the surface treatment layer after hotpressing is likely to peel off.

The content of the one or more selected from zirconia, lanthanum oxide,cerium oxide, and neodymium oxide in the surface treatment layer ispreferably more than or equal to 0.4 g/m² and less than or equal to 1.5g/m² per one surface.

Typical examples of the treatment liquid containing zirconia, lanthanumoxide, cerium oxide, and neodymium oxide include a zirconia sol, alanthanum oxide sol, a cerium oxide sol, and a neodymium oxide sol, andspecific examples of the commercially available product include NanoUse(registered trademark) series manufactured by Nissan ChemicalIndustries, Ltd. and Ceramase series manufactured by Taki Chemical Co.,Ltd.

Further, examples of the other component that is preferably furthercontained in the surface treatment layer according to the presentembodiment include magnesium oxide, calcium oxide, or zinc oxide.

When the surface treatment layer contains the above-mentioned magnesiumoxide, calcium oxide, or zinc oxide, those oxides are present on theouter layer of the surface treatment layer after hot pressing; and thus,phosphate treatability is improved. As a reason for the improvement inphosphate treatability, it is presumed that the chemical conversionreaction with a phosphate is accelerated by magnesium oxide beingdissolved in the phosphate treatment liquid. To obtain this effect moreefficiently, the particle size of each of the above-mentioned magnesiumoxide, calcium oxide, and zinc oxide is preferably more than or equal to5 nm and less than or equal to 100 nm, and more preferably more than orequal to 10 nm and less than or equal to 50 nm.

In the case where the surface treatment layer contains magnesium oxide,calcium oxide, or zinc oxide, the content thereof is preferably in therange of more than or equal to 0.2 g/m² and less than or equal to 5 g/m²per one surface, and more preferably more than or equal to 0.4 g/m² andless than or equal to 2.5 g/m² per one surface. In the case where thecontent of magnesium oxide, calcium oxide, or zinc oxide is less than0.2 g/m² per one surface, since those oxides are not sufficientlypresent after hot pressing, it may be difficult to exhibit satisfactoryphosphate treatability. On the other hand, in the case where the contentof magnesium oxide, calcium oxide, or zinc oxide exceeds 5 g/m² per onesurface, the cost of the Zn-based plated steel sheet according to thepresent embodiment is increased, and it is presumed that the cohesiveforce of the surface treatment layer is weakened and a coating film thatis formed on the surface treatment layer after hot pressing is likely topeel off.

The surface treatment layer according to the present embodiment maycontain, in addition to oxides like the above, at least one of one ormore P-containing compounds, one or more V-containing compounds, one ormore Cu-containing compounds, one or more Al-containing compounds, oneor more Si-containing compounds, and one or more Cr-containing compoundsdescribed in detail below in the range of a predetermined content.

The P-containing compound is a compound containing phosphorus as aconstituent element. Examples of the P-containing compound includecompounds such as phosphoric acid, phosphorous acid, phosphonic acid,phosphonous acid, phosphinic acid, phosphinous acid, a phosphine oxide,and phosphine, an ionic compound containing any of these compounds as ananion, and the like. All these P-containing compounds are commerciallyavailable as reagents or products, and can be easily obtained. TheseP-containing compounds exist in a state of being dissolved in atreatment liquid or in a state of being dispersed as powder in atreatment liquid, and exist, in the surface treatment layer, in a stateof being dispersed as solid.

The V-containing compound is a compound containing vanadium as aconstituent element. Examples of the V-containing compound includevanadium oxides such as vanadium pentoxide, metavanadic acid-basedcompounds such as ammonium metavanadate, vanadium compounds such assodium vanadate, and other V-containing compounds. Those V-containingcompounds are commercially available as reagents or products, and can beeasily obtained. Those V-containing compounds exist in a state of beingdissolved in a treatment liquid or in a state of being dispersed aspowder in a treatment liquid, and exist, in the surface treatment layer,in a state of being dispersed as solid.

The surface treatment layer according to the present embodimentpreferably contains one or more compounds selected from one or moreP-containing compounds and one or more V-containing compounds mentionedabove individually in the range of more than or equal to 0.0 g/m² andless than or equal to 0.01 g/m² per one surface on a P and V basis.

One or more compounds selected from one or more P-containing compoundsand one or more V-containing compounds mentioned above are oxidized intoan oxide during hot pressing, and the oxide exists locally at theinterface between the Zn-based plating layer and the surface treatmentlayer and forms an oxide layer that contains at least one of P and V andhas weak cohesive force. Since the content of the one or more compoundsselected from one or more P-containing compounds and one or moreV-containing compounds contained is individually in the range of morethan or equal to 0.0 g/m² and less than or equal to 0.01 g/m² per onesurface on a P and V basis, the thickness of an oxide layer like theabove that is formed during hot pressing and has weak cohesive force isreduced, and the adhesiveness between the Zn-based plating layer and thesurface treatment layer after hot pressing is further improved.

In the case where the content of the one or more selected from one ormore P-containing compounds and one or more V-containing compounds inthe surface treatment layer exceeds 0.01 g/m² per one surface, thethickness of the oxide layer that is formed during hot pressing and hasweak cohesive force is increased; consequently, the adhesiveness betweenthe Zn-based plating layer and the surface treatment layer is reduced,and as a result also adhesiveness after electrodeposition coating isreduced. From the viewpoint of the adhesiveness between the Zn-basedplating layer and the surface treatment layer after hot pressing, thecontent of the one or more compounds selected from one or moreP-containing compounds and one or more V-containing compounds in thesurface treatment layer is more preferably individually more than orequal to 0.0 g/m² and less than or equal to 0.003 g/m² per one surfaceon a P and V basis.

The Cu-containing compound is a compound containing copper as aconstituent element. Examples of the Cu-containing compound includemetal Cu, copper oxide, various organic copper compounds, variousinorganic copper compounds, and various copper complexes. ThoseCu-containing compounds are commercially available as reagents orproducts, and can be easily obtained. Those Cu-containing compoundsexist in a state of being dissolved in a treatment liquid or in a stateof being dispersed as powder in a treatment liquid, and exist, in thesurface treatment layer, in a state of being dispersed as solid.

The surface treatment layer according to the present embodimentpreferably contains one or more compounds selected from one or moreCu-containing compounds mentioned above in the range of more than orequal to 0.0 g/m² and less than or equal to 0.02 g/m² per one surface ona Cu basis.

One or more compounds selected from one or more Cu-containing compoundsmentioned above are oxidized into an oxide during hot pressing, and theoxide exists locally at the interface between the Zn-based plating layerand the surface treatment layer and forms an oxide layer that containsCu and has weak cohesive force. Since the content of the one or morecompounds selected from one or more Cu-containing compounds is in therange of more than or equal to 0.0 g/m² and less than or equal to 0.02g/m² per one surface on a Cu basis, the thickness of an oxide layer likethe above that is formed during hot pressing and has weak cohesive forceis reduced, and the adhesiveness between the Zn-based plating layer andthe surface treatment layer after hot pressing is further improved.

In the case where the content of the one or more selected from one ormore Cu-containing compounds in the surface treatment layer exceeds 0.02g/m² per one surface, the thickness of the oxide layer that is formedduring hot pressing and has weak cohesive force is increased;consequently, the adhesiveness between the Zn-based plating layer andthe surface treatment layer is reduced, and as a result, alsoadhesiveness after electrodeposition coating is reduced. In addition,since Cu is an element nobler than Fe, which is a main component of theground steel sheet, also the corrosion resistance tends to decrease.From the viewpoint of the adhesiveness between the Zn-based platinglayer and the surface treatment layer after hot pressing, the content ofthe one or more compounds selected from one or more Cu-containingcompounds in the surface treatment layer is more preferably more than orequal to 0.0 g/m² and less than or equal to 0.005 g/m² per one surfaceon a Cu basis.

The Al-containing compound is a compound containing aluminum as aconstituent element. Examples of the Al-containing compound includemetal Al, aluminum oxide, aluminum hydroxide, an ionic compoundcontaining an aluminum ion as a cation, and the like. ThoseAl-containing compounds are commercially available as reagents orproducts, and can be easily obtained. Those Al-containing compoundsexist in a state of being dissolved in a treatment liquid or in a stateof being dispersed as powder in a treatment liquid, and exist, in thesurface treatment layer, in a state of being dispersed as solid.

The Si-containing compound is a compound containing silicon as aconstituent element. Examples of the Si-containing compound include Sisimple substance, silica (silicon oxide), organic silane, a siliconeresin used also as a binder resin, and other Si-containing compounds.All these Si-containing compounds are commercially available as reagentsor products, and can be easily obtained. These Si-containing compoundsexist in a state of being dissolved in a treatment liquid or in a stateof being dispersed as powder in a treatment liquid, and exist, in thesurface treatment layer, in a state of being dispersed as solid.

The surface treatment layer according to the present embodimentpreferably contains one or more compounds selected from one or moreAl-containing compounds and one or more Si-containing compounds like theabove individually in the range of more than or equal to 0.0 g/m² andless than or equal to 0.005 g/m² per one surface on an Al and Si basis.

One or more compounds selected from one or more Al-containing compoundsand one or more Si-containing compounds like the above are oxidized intoan oxide during hot pressing, and the oxide concentrates on the surfaceof the surface treatment layer. Since the amount of the one or morecompounds selected from one or more Al-containing compounds and one ormore Si-containing compounds contained is individually in the range ofmore than or equal to 0.0 g/m² and less than or equal to 0.005 g/m² perone surface on an Al and Si basis, the existence ratio of the oxidescontaining Al or Si that are formed on the surface of the surfacetreatment layer during hot pressing is reduced, and the adhesivenessbetween the surface treatment layer and the electrodeposition coatingfilm after hot pressing is further improved.

In the case where the content of the one or more selected from one ormore Al-containing compounds and one or more Si-containing compounds inthe surface treatment layer is more than 0.005 g/m² per one surface, theexistence ratio of the oxides containing Al or Si that are formed duringhot pressing is increased. These oxides containing Al or Si inhibit theformation of a chemical conversion treatment coating film, and reducethe adhesiveness between the surface treatment layer and theelectrodeposition coating film after hot pressing; therefore, when theexistence ratio of the oxides containing Al or Si that are formed duringhot pressing is increased, the adhesiveness between the surfacetreatment layer and the electrodeposition coating film is reduced. Fromthe viewpoint of the adhesiveness between the surface treatment layerand the electrodeposition coating film after hot pressing (that is,post-coating adhesiveness), the amount of the one or more compoundsselected from one or more Al-containing compounds and one or moreSi-containing compounds contained in the surface treatment layer is morepreferably individually more than or equal to 0.0 g/m² and less than orequal to 0.002 g/m² per one surface on an Al and Si basis.

The Cr-containing compound is a compound containing chromium as aconstituent element. Examples of the Cr-containing compound includemetal Cr, chromium compounds having various valences, and an ioniccompound containing a chromium ion having any of various valences as acation. Those Cr-containing compounds exist in a state of beingdissolved in a treatment liquid or in a state of being dispersed aspowder in a treatment liquid, and exist, in the surface treatment layer,in a state of being dispersed as solid.

The Cr-containing compound varies in performance and properties inaccordance with the valence, and many hexavalent chromium compounds areharmful. In view of the current tendency of attention to environmentalprotection being strongly required, the surface treatment layeraccording to the present embodiment preferably contains as little amountof Cr-containing compounds mentioned above as possible, and is morepreferably chromium-free.

From the view point mentioned above, the surface treatment layeraccording to the present embodiment preferably contains one or morecompounds selected from Cr-containing compounds like the above in therange of more than or equal to 0.0 g/m² and less than or equal to 0.01g/m² per one surface on an Cr basis, and is more preferablychromium-free.

The surface treatment layer may contain pigments such as carbon blackand titania, various anti-corrosive particles used for coated steelsheets, and the like as long as the effect of the present inventionbased on containing one or more oxides selected from titanium oxide,nickel oxide, and tin(IV) oxide is not inhibited. Also in this case, thesurface treatment layer contains the one or more oxides selected fromtitanium oxide, nickel oxide, and tin(IV) oxide in the range of morethan or equal to 0.2 g/m² and less than or equal to 2 g/m² per onesurface.

As the method for forming the surface treatment layer, a treatmentliquid containing one or more oxides selected from titanium oxide,nickel oxide, and tin(IV) oxide may be applied to the surface of azinc-plated steel sheet, and drying and baking may be performed.

The coating method is not limited to a specific method, and examplesinclude a method in which a ground steel sheet is dipped in a treatmentliquid or a treatment liquid is sprayed to the surface of a ground steelsheet, and then the attached amount is controlled by a roll or gasspraying so as to obtain a prescribed attached amount, and a method ofcoating using a roll coater or a bar coater.

The method of drying and baking is not limited to a specific method,either, as long as it is a method that can volatilize a dispersionmedium (mainly water). Here, if heating is performed at an excessivelyhigh temperature, it is feared that the uniformity of the surfacetreatment layer will be reduced; conversely, if heating is performed atan excessively low temperature, it is feared that productivity will bereduced. Thus, to produce a surface treatment layer having excellentcharacteristics stably and efficiently, the surface treatment layerafter coating is preferably heated at a temperature of approximately 80°C. to 150° C. for approximately 5 seconds to 20 seconds.

The formation of the surface treatment layer is preferably performedin-line in the production line of the plated steel sheet because this iseconomical; but the surface treatment layer may be formed also inanother line, or may be formed after blanking for molding is performed.

Here, the content of the one or more oxides selected from titaniumoxide, nickel oxide, and tin(IV) oxide in the surface treatment layercan be measured by a known method; for example, the fact that thevarious compounds are the one or more oxides selected from titaniumoxide, nickel oxide, and tin(IV) oxide is checked beforehand bycross-sectional energy dispersive X-ray (EDX) analysis or the like, andthen the coating film is dissolved; thus, the measurement can be madeusing inductively coupled plasma (ICP) emission spectrometric analysisor the like. Also, the content of other oxides that are preferablycontained in the surface treatment layer, and the content of theabove-mentioned one or more P-containing compounds, V-containingcompounds, Cu-containing compounds, Al-containing compounds,Si-containing compounds, and Cr-containing compounds contained in thesurface treatment layer can be measured by a similar method.

<2. Regarding Hot Pressing Process>

In the case where the hot pressing method is used for a hot-dip Zn-basedplated steel sheet like that described above, the hot-dip Zn-basedplated steel sheet is heated to a prescribed temperature, and is thenpress-molded. In the case of the hot-dip Zn-based plated steel sheetaccording to the present embodiment, heating is usually performed to 700to 1000° C. because hot press molding is performed; but in the casewhere a martensite single phase is formed after rapid cooling ormartensite is formed at a volume ratio of 90% or more, it is importantthat the lower limit of the heating temperature be the Ac₃ point ormore. In the case of the present invention, also the case where atwo-phase region of martensite/ferrite is formed after rapid cooling isincluded, and therefore the heating temperature is preferably 700 to1000° C. as described above.

Examples of the hot pressing method include two methods of hot pressingby slow heating and hot pressing by rapid heating. Examples of theheating method used include heating with an electric furnace or a gasfurnace, flame heating, energization heating, high-frequency heating,and induction heating, and the atmosphere during heating is notparticularly limited; as a heating method to obtain the effect of thepresent invention significantly, energization heating, inductionheating, and the like, which are rapid heating, are preferably used.

In the hot pressing method by slow heating, the radiation heating of aheating furnace is used. First, the hot-dip Zn-based plated steel sheetaccording to the present embodiment that is used as a steel sheet forhot pressing is placed in a heating furnace (a gas furnace, an electricfurnace, or the like). The steel sheet for hot pressing is heated at 700to 1000° C. in the heating furnace, and is, depending on the condition,kept at this heating temperature (soaking). Thereby, molten Zn in thehot-dip Zn-based plating layer is combined with Fe and forms a solidphase (Fe—Zn solid solution phase). After the molten Zn in the hot-dipZn-based plating layer is combined with Fe and forms a solid phase, thesteel sheet is taken out of the heating furnace. Alternatively, bycombining molten Zn in the hot-dip Zn-based plating layer with Fe bysoaking, the solid phase may be formed as an Fe—Zn solid solution phaseand a ZnFe alloy phase; and then the steel sheet may be taken out of theheating furnace.

Alternatively, the Zn-based plated steel sheet may be heated to 700 to1000° C. while no keeping time is provided or the keeping time is set toa short time, and the steel sheet may be taken out of the heatingfurnace. In this case, after the steel sheet is heated to 700 to 1000°C., cooling is performed without applying stress to the steel sheet bypress molding or the like until Zn in the Zn-based plating layer iscombined with Fe and forms a solid phase (Fe—Zn solid solution phase orZnFe alloy phase). Specifically, cooling is performed until at least thetemperature of the steel sheet becomes lower than or equal to 782° C.After the cooling, as described below, cooling is performed while thesteel sheet is pressed using a mold.

Also in hot pressing by rapid heating, similarly, the Zn-based platedsteel sheet according to the present embodiment that is used as a steelsheet for hot pressing is rapidly heated to 700 to 1000° C. The rapidheating is performed by, for example, energization heating or inductionheating. The average heating rate in this case is 20° C./second or more.In the case of rapid heating, after the Zn-based plated steel sheethot-dip Zn-based plated steel sheet is heated to 700 to 1000° C.,cooling is performed without applying stress to the steel sheet by pressmolding or the like until Zn in the Zn-based plating layer is combinedwith Fe and forms a solid phase (Fe—Zn solid solution phase or ZnFealloy phase). Specifically, cooling is performed until at least thetemperature of the steel sheet becomes lower than or equal to 782° C.After the cooling, as described below, cooling is performed while thesteel sheet is pressed using a mold.

The taken-out steel sheet is pressed using a mold. When pressing thesteel sheet, the steel sheet is cooled by the mold. A cooling medium(for example, water or the like) is circulated through the mold, and themold removes heat from the steel sheet and cools it. By the aboveprocess, a hot pressed steel material is produced by normal heating.

The hot pressed steel material produced using the Zn-based plated steelsheet having the surface treatment layer according to the presentembodiment can exhibit satisfactory post-coating adhesiveness, becauseeven if chemical conversion treatment after hot pressing is insufficientdue to influences of treatment time, concentration, temperature, and thelike, one or more oxides selected from titanium oxide, nickel oxide, andtin(IV) formed on the surface of the steel sheet exhibit excellentadhesiveness with the electrodeposition coating film.

EXAMPLES

The action and effect of the Zn-based plated steel sheet according to anembodiment of the present invention will now be described still morespecifically with reference to Examples. Examples shown below are onlyexamples of the Zn-based plated steel sheet according to the presentinvention, and the Zn-based plated steel sheet according to the presentinvention is not limited to Examples below.

<Ground Steel Sheet>

In the following, first, pieces of molten steel having the chemicalcompositions shown in Table 1 below were produced. After that, theproduced pieces of molten steel were used to produce slabs by thecontinuous casting method. The obtained slab was hot rolled to produce ahot rolled steel sheet. Subsequently, the hot rolled steel sheet waspickled, and then cold rolling was performed to produce a cold rolledsteel sheet; thus, steel sheets of steel #1 to #8 having the chemicalcompositions described in Table 1 were prepared. As shown in Table 1,the sheet thicknesses of the steel sheets of all the steel types were1.6 mm.

TABLE 1 Sheet Type of thickness Chemical composition (mass %, thebalance: Fe and impurities) steel (mm) C Si Mn P S sol.Al N B Ti Cr MoNb Ni #1 1.6 0.2 0.2 1.3 0.01 0.005 0.02 0.002 0.002 0.02 0.2 — — — #21.6 0.2 0.5 1.3 0.01 0.005 0.02 0.002 0.002 0.02 0.2 — — — #3 1.6 0.20.5 1.3 0.01 0.005 0.02 0.002 0.002 0.02 0.2 — 0.05 — #4 1.6 0.2 0.5 1.30.01 0.005 0.02 0.002 0.002 0.02 0.2 — — 1 #5 1.6 0.2 0.5 1.3 0.01 0.0050.02 0.002 0.002 0.02 0.2 0.5 — — #6 1.6 0.2 0.5 1.3 0.01 0.005 0.020.002 — — — — — — #7 1.6 0.2 0.2 0.2 0.01 0.005 0.02 0.002 0.002 0.020.2 — — — #8 1.6 0.2 0.2 0.4 0.01 0.005 0.02 0.002 0.002 0.02 0.2 — — —<Zn-Based Plating Layer>

The steel sheets of steel #1 to #8 were subjected to hot-dip galvanizingtreatment, and were then subjected to alloying treatment. With themaximum temperature in each alloying treatment set to 530° C., heatingwas performed for approximately 30 seconds; and then cooling wasperformed to room temperature; thus, an alloyed hot-dip galvanized steelsheet (GA) was produced. Using steel #1, hot-dip galvanizing treatmentwas performed, and a hot-dip galvanized steel sheet (GI) was producedwithout performing alloying treatment.

Further, steel #1 was subjected to various types of hot-dip galvanizingusing three types of plating baths of molten Zn-55% Al, molten Zn-6%Al-3% Mg, and molten Zn-11% Al-3% Mg-0.2% Si, and hot-dip zinc-basedplated steel sheets A1 to A3 were produced.

A1: molten Zn-55% Al

A2: molten Zn-6% Al-3% Mg

A3: molten Zn-11% Al-3% Mg-0.2% Si

In addition, steel #1 was subjected to various types of Zn-based platingof Zn electroplating, Zn—Ni electroplating, and Zn—Co electroplating.

Note that, as a specific plating operation in the case of usingelectroplating, electrolysis treatment was performed in an electrolytesolution containing Zn ions, using the steel sheet, as a negativeelectrode, and a counter electrode. The amount of plating attached tothe steel sheet was controlled by the composition of the electrolytesolution, the current density, and the electrolysis time.

A4: Zn electroplating

A5: Zn—Ni electroplating

A6: Zn—Co electroplating

In the eight types of Zn-based plating processes mentioned above, theamount of the Zn-based plating layer attached was equally set to 60 g/m²per one surface.

<Surface Treatment Layer>

Subsequently, in order to prepare a chemical solution having thecompositions shown in Table 2 in a solid content ratio, the followingoxides and chemical agents were blended using water. The obtainedtreatment liquid was applied with a bar coater, and drying was performedusing an oven under conditions for keeping a maximum peak temperature of100° C. for 8 seconds; thus, a plated steel sheet for hot pressing wasproduced. The amount of the treatment liquid attached was adjusted bythe dilution of the liquid and the count of the bar coater so that thetotal amount of attached nonvolatile content in the treatment liquidmight be the numerical value shown in Table 3. In Table 2 below, thesolid content concentration of each component is written as the ratio ofthe nonvolatile content of each component, such as “oxide A,” to thenonvolatile content of the entire treatment liquid (unit:mass %).

The components (symbols) in Table 2 are as follows.

As described later, also a treatment liquid containing alumina (sol) wasinvestigated as granular substances other than titanium oxide, nickeloxide, and tin(IV) oxide; in this case, alumina is denoted by “oxide A”.Similarly, zirconia, lanthanum oxide, cerium oxide, and neodymium oxideare denoted by “oxide B”, and magnesium oxide, calcium oxide, and zincoxide are denoted by “oxide C”.

(Oxide A) titanium oxide, nickel oxide, tin(IV) oxide, and alumina

TPA: titania powder (manufactured by IoLiTec GmbH), particle size: 10 to30 nm (catalog value)

TPB: titania powder (TITANIX JA-1, manufactured by Tayca Corporation),particle size: 180 nm (catalog value)

Ti: titania sol (titania sol TKS-203, manufactured by TaycaCorporation), particle size: 6 nm (catalog value)

Ni: nickel oxide (nickel oxide, manufactured by IoLiTec GmbH), particlesize 20 nm

NP: nickel oxide (nickel oxide, manufactured by Japan Pure Chemical Co.,Ltd.), particle size: approximately 7 μm

Sn: tin(IV) oxide sol (Ceramase C-10, manufactured by Taki Chemical Co.,Ltd.), particle size: 10 nm

SP: tin(IV) oxide (tin oxide, manufactured by IoLiTec GmbH), particlesize: 10 to 20 nm

AZ: an alumina sol (alumina sol 200, manufactured by Nissan ChemicalIndustries, Ltd.), particle size: approximately 10 nm

(Oxide B) zirconia, lanthanum oxide, cerium oxide, and neodymium oxide

ZA: a zirconia sol (NanoUse (registered trademark) ZR-30AL, manufacturedby Nissan Chemical Industries, Ltd.), particle size: 70 to 110 nm(catalog value)

La: a lanthanum oxide sol (Biral La-C10, manufactured by Taki ChemicalCo., Ltd.), particle size: 40 nm (catalog value)

Ce: a cerium oxide sol (Needlal P-10, manufactured by Taki Chemical Co.,Ltd.), particle size: 20 nm (catalog value)

Nd: a neodymium oxide sol (Biral Nd-C10, manufactured by Taki ChemicalCo., Ltd.), particle size: 40 nm (catalog value)

(Oxide C) magnesium oxide, calcium oxide, and zinc oxide

Mg: magnesium oxide (manufactured by IoLiTec GmbH), particle size: 35 nm(catalog value)

Ca: calcium oxide (manufactured by Kanto Chemical Co., Inc.)

*Used after being dispersed in resin-added water and pulverizing pigmentwith a ball mill.

Zn: zinc oxide (manufactured by IoLiTec GmbH), particle size: 20 nm(catalog value)

(iii) Resin

A: a urethane-based resin emulsion (Superflex (registered trademark)150, manufactured by DKS Co. Ltd.)

B: a urethane-based resin emulsion (Superflex (registered trademark)E-2000, manufactured by DKS Co. Ltd.)

C: a polyester resin emulsion (Vylonal (registered trademark) MD1480,manufactured by Toyobo Co., Ltd.)

(iv) Crosslinking Agent

M: a melamine resin (Cymel (registered trademark) 325, manufactured byMitsui Cytec Ltd.)

Z: ammonium zirconium carbonate (an ammonium zirconium carbonatesolution, manufactured by Kishida Chemical Co., Ltd.)

S: a silane coupling agent (Sila-Ace S510, manufactured by NichibiTrading Co., LTD.) (a Si-containing compound)

(v) Pigment

CB: carbon black (Mitsubishi (registered trademark) carbon black #1000,manufactured by Mitsubishi Chemical Corporation)

T: titanium oxide (titanium oxide R-930, manufactured by Ishihara SangyoKaisha, Ltd.), particle size: 250 nm (catalog value)

“T” titanium oxide described herein is a pigment with a particle size of200 to 400 nm mainly used for a white pigment or the like in a coatingmaterial, and cannot achieve performance obtained by oxide B because theparticle size is larger than that of (oxide A).

PA: condensed Al phosphate (condensed aluminum phosphate, K-WhiteZF150W, manufactured by Tayca Corporation) (a P and Al-containingcompound)

PZ: zinc phosphite (NP-530, manufactured by Toho Ganryo Co., Ltd.) (aP-containing compound)

Si1: silica particles (Sylomask 02, manufactured by Fuji SilysiaChemical Ltd.) (a Si-containing compound)

Si2: colloidal silica (Snowtex O, manufactured by Nissan ChemicalIndustries, Ltd.) (a Si-containing compound)

Al: an alumina sol (AS-200, manufactured by Nissan Chemical Industries,Ltd.) (an Al-containing compound)

V: potassium vanadate (a general reagent) (a V-containing compound)

Cr: Cr(VI) oxide (a general reagent) (a Cr-containing compound)

Cu: copper(II) oxide (a general reagent) (a Cu-containing compound)

TABLE 2 Oxide A Oxide B Oxide C Resin Crosslinking agent Pigment, etc.Concen- Concen- Concen- Concen- Concen- Concen- tration tration trationtration tration tration Type (mass %) Type (mass %) Type (mass %) Type(mass %) Type (mass %) Type (mass %) Notes 1 Ti 100 — 0 — 0 — 0 — 0 — 02 Ti 75 — 0 — 0 B 25 — 0 — 0 3 Ti 40 — 0 — 0 B 60 — 0 — 0 4 Ti 20 — 0 —0 B 80 — 0 — 0 5 Ti 50 — 0 — 0 B 50 — 0 — 0 6 Ti 50 — 0 — 0 B 45 Z 5 — 07 Ti 50 — 0 — 0 B 45 S 5 — 0 8 Ti 50 — 0 — 0 B 45 — 0 CB 5 9 Ti 50 — 0 —0 B 45 — 0 T 5 10 Ti 50 — 0 — 0 B 40 — 0 PA 10 11 Ti 50 — 0 — 0 B 40 — 0Si 10 12 TPA 100 — 0 — 0 — 0 — 0 — 0 13 TPA 50 — 0 — 0 A 50 — 0 — 0 14TPB 100 — 0 — 0 — 0 — 0 — 0 15 TPB 50 — 0 — 0 A 50 — 0 — 0 16 Ni 50 — 0— 0 B 50 — 0 — 0 17 Sn 50 — 0 — 0 B 50 — 0 — 0 18 SP 50 — 0 — 0 B 50 — 0— 0 19 NP 50 — 0 — 0 B 50 — 0 — 0 20 Ti:Ni = 1:1 50 — 0 — 0 B 50 — 0 — 021 Ti:Ni = 1:1 50 — 0 — 0 B 40 — 0 PA 10 22 Ti:Sn = 1:1 50 — 0 — 0 B 50— 0 — 0 23 Ti:Sn = 11 50 — 0 — 0 B 40 — 0 PA 10 24 Ti:SP = 1:1 50 — 0 —0 B 50 — 0 — 0 25 Ti:SP = 1:1 50 — 0 — 0 B 40 — 0 PA 10 26 Ti:Ni:Sn =1:1:1 60 — 0 — 0 B 40 — 0 — 0 27 Ti:Ni:SP = 1:1:1 60 — 0 — 0 B 40 — 0 —0 28 Ni:Sn:SP = 1:1:1 60 — 0 — 0 B 40 — 0 — 0 29 AZ 100 — 0 — 0 — 0 — 0— 0 30 AZ 50 — 0 — 0 B 50 — 0 — 0 31 — 0 — 0 — 0 A 100 — 0 — 0 32 — 0 —0 — 0 — 0 — 0 — 0 33 Ti 25 ZA 25 — 0 B 35 S 5 PA 10 34 Ti 25 ZA 25 — 0 B35 S 5 Si 10 35 Ti 25 ZA 25 — 0 B 35 Z 5 PA 10 36 Ti 25 ZA 25 — 0 B 35 Z5 Si 10 37 Ti 30 ZA 30 — 0 B 40 — 0 — 0 38 Ti 30 La 30 — 0 B 40 — 0 — 039 Ti 30 Ce 30 — 0 B 40 — 0 — 0 40 Ti 30 Nd 30 — 0 B 40 — 0 — 0 41 Ti 20ZA 50 — 0 B 30 — 0 — 0 42 Ti 10 ZA 50 — 0 B 40 — 0 — 0 43 Ti 5 ZA 5 — 0B 90 — 0 — 0 44 Ti 30 ZA 50 — 0 B 20 — 0 — 0 45 Ni 30 ZA 30 — 0 B 40 — 0— 0 46 Sn 30 ZA 30 — 0 B 40 — 0 — 0 47 Ti 20 — 0 Mg 30 B 35 S 5 PA 10 48Ti 20 — 0 Mg 30 B 35 S 5 Si 10 49 Ti 20 — 0 Mg 30 B 35 Z 5 PA 10 50 Ti20 — 0 Mg 30 B 35 Z 5 Si 10 51 Ti 25 — 0 Mg 35 B 40 — 0 — 0 52 Ni 25 — 0Mg 35 B 40 — 0 — 0 53 Ni 20 — 0 Mg 30 B 35 S 5 PA 10 54 Ni 20 — 0 Mg 30B 35 S 5 Si 10 55 Sn 25 — 0 Mg 35 B 40 — 0 — 0 56 Sn 20 — 0 Mg 30 B 35 S5 PA 10 57 SP 50 — 0 Mg 20 B 30 — 0 — 0 58 SP 20 — 0 Mg 30 B 35 S 5 PA10 59 Ti 5 — 0 Mg 5 B 90 — 0 — 0 60 Ti 50 — 0 Mg 30 B 20 — 0 — 0 61 Ti20 ZA 20 Mg 30 B 30 — 0 — 0 62 Ni 20 ZA 20 Mg 30 B 30 — 0 — 0 63 Sn 20ZA 20 Mg 30 B 30 — 0 — 0 64 Ti 20 La 20 Mg 30 B 30 — 0 — 0 65 Ti 20 Ce20 Mg 30 B 30 — 0 — 0 66 Ti 20 Nd 20 Mg 30 B 30 — 0 — 0 67 Ti 20 ZA 20Mg 30 B 20 S 5 PA 5 68 Ti 20 ZA 20 Mg 30 B 20 S 5 Si 5 69 Ti 20 ZA 20 Mg30 B 20 Z 5 PA 5 70 Ti 20 Za 20 Mg 30 B 20 Z 5 Si 5 71 Ti 20 La 20 Mg 30B 20 S 5 PA 5 72 Ti 20 La 20 Mg 30 B 20 S 5 Si 5 73 Ti 20 La 20 Mg 30 B20 Z 5 PA 5 74 Ti 20 La 20 Mg 30 B 20 Z 5 Si 5 75 Ti 25 Ca 35 B 40 — 0 —0 76 Ti 25 Zn 35 B 40 — 0 — 0 77 Ti 20 ZA 20 Ca 30 B 30 — 0 — 0 78 Ti 20ZA 20 Zn 30 B 30 — 0 — 0 79 Ni 20 ZA 20 Ca 30 B 30 — 0 — 0 80 Ni 20 ZA20 Zn 30 B 30 — 0 — 0 81 Sn 20 ZA 20 Ca 30 B 30 — 0 — 0 82 Sn 20 ZA 20Zn 30 B 30 — 0 — 0 83 Ti:Ni = 1:1 30 ZA 30 — 0 B 40 — 0 — 0 84 Ti:Sn =1:1 30 ZA 30 — 0 B 40 — 0 — 0 85 Ti:SP = 1:1 30 ZA 30 — 0 B 40 — 0 — 086 Ti:Ni:Sn = 1:1:1 30 ZA 30 — 0 B 40 — 0 — 0 87 Ti:Ni = 1:1 30 La 30 —0 B 40 — 0 — 0 88 Ti:Sn = 1:1 30 La 30 — 0 B 40 — 0 — 0 89 Ti:SP = 1:130 La 30 — 0 B 40 — 0 — 0 90 Ti:Ni:Sn = 1:1:1 30 La 30 — 0 B 40 — 0 — 091 Ti:Ni = 1:1 30 ZA:La = 1:1 30 — 0 B 40 — 0 — 0 92 Ti:Sn = 1:1 30ZA:La = 1:1 30 — 0 B 40 — 0 — 0 93 Ti:SP = 1:1 30 ZA:La = 1:1 30 — 0 B40 — 0 — 0 94 Ti:Ni:Sn = 1:1:1 30 ZA:La = 1:1 30 — 0 B 40 — 0 — 0 95Ti:Ni = 1:1 20 ZA 20 Mg 30 B 30 — 0 — 0 96 Ti:Ni = 1:1 20 ZA 20 Mg 30 B30 — 0 — 0 97 Ti 50 — 0 — 0 B 48 — 0 Al 2 98 Ti 50 — 0 — 0 B 49.1 — 0 Al0.9 99 Ti 50 — 0 — 0 B 49.7 — 0 Al 0.3 100 Ti 50 — 0 — 0 B 48 — 0 Si2 2101 Ti 50 — 0 — 0 B 49 — 0 Si2 1 102 Ti 50 — 0 — 0 B 49.7 — 0 Si2 0.3103 Ti 50 — 0 — 0 B 45 — 0 PZ 5 104 Ti 50 — 0 — 0 B 48 — 0 PZ 2 105 Ti50 — 0 — 0 B 49.5 — 0 PZ 0.5 106 Ti 50 — 0 — 0 B 46 — 0 V 4 107 Ti 50 —0 — 0 B 48 — 0 V 2 108 Ti 50 — 0 — 0 B 49.5 — 0 V 0.5 109 Ti 50 — 0 — 0B 46 — 0 Cu 4 110 Ti 50 — 0 — 0 B 48 — 0 Cu 2 111 Ti 50 — 0 — 0 B 49.5 —0 Cu 0.5 112 Ti 50 — 0 — 0 B 48 — 0 Cr 2 113 Ti 50 — 0 — 0 B 49.2 — 0 Cr0.8 114 Ti 30 ZA 30 — 0 B 49 — 0 Al 1 115 Ti 30 ZA 30 — 0 B 49.6 — 0 Al0.4 116 Ti 30 ZA 30 — 0 B 49.9 — 0 Al 0.1 117 Ti 30 ZA 30 — 0 B 49 — 0Si2 1 118 Ti 30 ZA 30 — 0 B 49.5 — 0 Si2 0.5 119 Ti 30 ZA 30 — 0 B 49.9— 0 Si2 0.1 120 Ti 30 ZA 30 — 0 B 47 — 0 PZ 3 121 Ti 30 ZA 30 — 0 B 49 —0 PZ 1 122 Ti 30 ZA 30 — 0 B 49.8 — 0 PZ 0.2 123 Ti 30 ZA 30 — 0 B 48 —0 V 2 124 Ti 30 ZA 30 — 0 B 49 — 0 V 1 125 Ti 30 ZA 30 — 0 B 49.8 — 0 V0.2 126 Ti 30 ZA 30 — 0 B 48 — 0 Cu 2 127 Ti 30 ZA 30 — 0 B 49 — 0 Cu 1128 Ti 30 ZA 30 — 0 B 49.8 — 0 Cu 0.2 129 Ti 30 ZA 30 — 0 B 49 — 0 Cr 1130 Ti 30 ZA 30 — 0 B 49.6 — 0 Cr 0.4 131 Ti 25 — 0 Mg 35 B 49.2 — 0 Al0.8 132 Ti 25 — 0 Mg 35 B 49.6 — 0 Al 0.4 133 Ti 25 — 0 Mg 35 B 49.9 — 0Al 0.1 134 Ti 25 — 0 Mg 35 B 49.2 — 0 Si2 0.8 135 Ti 25 — 0 Mg 35 B 49.6— 0 Si2 0.4 136 Ti 25 — 0 Mg 35 B 49.9 — 0 Si2 0.1 137 Ti 25 — 0 Mg 35 B47 — 0 PZ 3 138 Ti 25 — 0 Mg 35 B 49 — 0 PZ 1 139 Ti 25 — 0 Mg 35 B 49.6— 0 PZ 0.4 140 Ti 25 — 0 Mg 35 B 48 — 0 V 2 141 Ti 25 — 0 Mg 35 B 49 — 0V 1 142 Ti 25 — 0 Mg 35 B 49.7 — 0 V 0.3 143 Ti 25 — 0 Mg 35 B 48 — 0 Cu2 144 Ti 25 — 0 Mg 35 B 49 — 0 Cu 1 145 Ti 25 — 0 Mg 35 B 49.8 — 0 Cu0.2 146 Ti 25 — 0 Mg 35 B 48.5 — 0 Cr 1.5 147 Ti 25 — 0 Mg 35 B 49.5 — 0Cr 0.5 148 Ti 20 ZA 20 Mg 30 B 49.3 — 0 Al 0.7 149 Ti 20 ZA 20 Mg 30 B49.7 — 0 Al 0.3 150 Ti 20 ZA 20 Mg 30 B 49.9 — 0 Al 0.1 151 Ti 20 ZA 20Mg 30 B 49.4 — 0 Si2 0.6 152 Ti 20 ZA 20 Mg 30 B 49.7 — 0 Si2 0.3 153 Ti20 ZA 20 Mg 30 B 49.9 — 0 Si2 0.1 154 Ti 20 ZA 20 Mg 30 B 48 — 0 PZ 2155 Ti 20 ZA 20 Mg 30 B 49.4 — 0 PZ 0.6 156 Ti 20 ZA 20 Mg 30 B 49.8 — 0PZ 0.2 157 Ti 20 ZA 20 Mg 30 B 48.8 — 0 V 1.2 158 Ti 20 ZA 20 Mg 30 B49.4 — 0 V 0.6 159 Ti 20 ZA 20 Mg 30 B 49.8 — 0 V 0.2 160 Ti 20 ZA 20 Mg30 B 48.8 — 0 Cu 1.2 161 Ti 20 ZA 20 Mg 30 B 49.4 — 0 Cu 0.6 162 Ti 20ZA 20 Mg 30 B 49.8 — 0 Cu 0.2 163 Ti 20 ZA 20 Mg 30 B 49 — 0 Cr 1 164 Ti20 ZA 20 Mg 30 B 49.5 — 0 Cr 0.5<Hot Pressing Process>

After the formation process of the surface treatment layer, the steelsheet of each test number was subjected to hot press heating by twotypes of heating systems of furnace heating and energization heating,and thus hot pressing was performed. In the furnace heating, theatmosphere in the furnace was set to 910° C. and the air-fuel ratio wasset to 1.1, and the steel sheet was taken out of the furnace immediatelyafter the temperature of the steel sheet reached 900° C. In theenergization heating, heating was performed at 870° C., with the heatingrate set to 85° C./second and 42.5° C./second. In the following, theresults of energization heating, which is heating of a shorter time thanfurnace heating, are shown in Table 3, and the results by furnaceheating are shown in Table 4.

After the hot press heating, cooling was performed until the temperatureof the steel sheet became 650° C. After the cooling, the steel sheet wassandwiched by a flat sheet mold equipped with a water cooling jacket,and thus a hot pressed steel material (steel sheet) was produced.Cooling was performed up to approximately 360° C., which is themartensite transformation starting point, so as to ensure a cooling rateof 50° C./second or more even in a portion where the cooling rate hadbeen low during the hot pressing, and thus quenching was performed.

<Evaluation Method>

[Phosphate Treatability Evaluation Test]

The sheet-like hot pressed steel material of each of the test numbersdescribed in Table 3 and Table 4 below was subjected to surfaceconditioning at room temperature for 20 seconds using a surfaceconditioning treatment agent, Prepalene X (product name) manufactured byNihon Parkerizing Co., Ltd. Further, phosphate treatment was performedusing a zinc phosphate treatment liquid, Palbond 3020 (product name)manufactured by Nihon Parkerizing Co., Ltd. The sheet-like hot pressedsteel material was dipped in the treatment liquid for 10 seconds or 30seconds, while it is normally 120 seconds, with the temperature of thetreatment liquid set to 43° C., and then water washing and drying wereperformed. The reason for making the time for dipping the material inthe treatment liquid shorter than the ordinary time for dipping thematerial in the treatment liquid is to imitate the situation in whichattached amount of phosphate treatment to be performed after that on thehot-dip Zn-based plated steel sheet is not sufficient.

Random 5 visual fields (125 μm×90 μm) of the surface of the hot pressedsteel material after phosphate treatment were observed with a scanningelectron microscope (SEM) at a magnification of 1000 times, and backscattered electron images (BSE images) were obtained. In the backscattered electron image, the observation area was displayed as an imageby the gray scale. In the back scattered electron image, the contrast isdifferent between a portion where a phosphate coating film that is achemical conversion coating film is formed and a portion where aphosphate coating film is not formed. Thus, the numerical range X1 ofthe lightness (a plurality of levels of gradation) of a portion where aphosphate coating film was not formed was determined in advance by a SEMand an energy dispersive X-ray spectrometer (EDS).

In the back scattered electron image of each visual field, the area A1of an area showing the contrast of the numerical range X1 was found byimage processing. Then, the transparent area ratio TR (%) of each visualfield was found on the basis of Formula (1) below.TR=(A1/A0)×100  (1)

Here, in Formula (1) above, A0 represents the total area of the visualfield (11,250 μm²). The average of the transparent area ratios TR (%) ofthe 5 visual fields was defined as the transparent area ratio (%) of thehot pressed steel material of the test number.

“M” in the “Phosphate treatability” section in Table 3 and Table 4 meansthat the transparent area ratio was more than or equal to 30%. “L” meansthat the transparent area ratio was more than or equal to 25% and lessthan 30%. “K” means that the transparent area ratio was more than orequal to 20% and less than 25%. “J” means that the transparent arearatio was more than or equal to 15% and less than 20%. “I” means thatthe transparent area ratio was more than or equal to 13% and less than15%. “H” means that the transparent area ratio was more than or equal to11% and less than 13%. “G” means that the transparent area ratio wasmore than or equal to 10% and less than 11%. “F” means that thetransparent area ratio was more than or equal to 8% and less than 10%.“E” means that the transparent area ratio was more than or equal to 6%and less than 8%. “D” means that the transparent area ratio was morethan or equal to 5% and less than 6%. “C” means that the transparentarea ratio was more than or equal to 2.5% and less than 5%. “B” meansthat the transparent area ratio was more than or equal to 1% and lessthan 2.5%. “A” means that the transparent area ratio was less than 1%.The case of “I,” “H,” “G,” “F,” “E,” “D,” “C,” “B,” or “A” in thetransparency evaluation was assessed as excellent in phosphatetreatability.

[FF Chemical Conversion Treatability Evaluation Test]

Further, instead of the phosphate treatability, treatment using anaqueous solution containing Zr ions and/or Ti ions, and fluorine andcontaining 100 to 1000 ppm of free fluoride ions (hereinafter, referredto as FF chemical conversion treatment liquid) was performed.

The FF chemical conversion treatment liquid mentioned above dissolvesfree fluorine (hereinafter, abbreviated as FF), an Al oxide coatingfilm, and a Zn oxide coating film. Therefore, while dissolving part orthe whole of the Al oxide coating film and the Zn oxide coating film, FFetches the Zn-containing layer formed in the hot stamping process. As aresult, a chemical conversion treatment layer made of an oxide of Zr andTi, or a mixture of an oxide and a fluoride of Zr and Ti (hereinafter,referred to as a specific chemical conversion treatment layer) isformed. When the FF concentration is controlled so that the Al oxidecoating film and the Zn oxide coating film can be etched, the Al oxidecoating film and the Zn oxide coating film are etched, and the specificchemical conversion treatment layer is formed.

To obtain the FF chemical conversion treatment liquid, H₂ZrF₆(hexafluorozirconic acid) and H₂TiF₆ (hexafluorotitanic acid) were putin a container so that the metal concentration might be a prescribedvalue, and were diluted with ion-exchanged water. After that,hydrofluoric acid and a sodium hydroxide aqueous solution were put inthe container, and adjustment was made so that the fluorineconcentration and the free fluorine concentration in the solution mightbe prescribed values. The free fluorine concentration was measured usinga commercially available concentration measuring device. After theadjustment, the container was adjusted to a fixed volume withion-exchanged water; thus, an FF chemical conversion treatment liquidwas prepared.

Regarding the FF chemical conversion treatment, as pre-treatment,dipping degreasing was performed at 45° C. for 2 minutes using analkaline degreasing agent (EC90, manufactured by Nippon Paint Co.,Ltd.). After that, dipping was performed in the FF chemical conversiontreatment liquids shown in Table 6 below at 40° C. for 10 seconds or 30seconds, while it is normally 120 seconds, and thus chemical conversiontreatment was performed. After the chemical conversion treatment, thetest piece was washed with water and dried. The reason for making thetime for dipping the material in the treatment liquid shorter than theordinary time for dipping the material in the treatment liquid is toimitate the situation in which attached amount of FF chemical conversiontreatment to be performed after that on the hot-dip Zn-based platedsteel sheet is not sufficient.

To investigate the chemical conversion treatability of the specificchemical conversion treatment layer of the resulting test material, theamount of Zr or Ti attached was measured by fluorescent X-ray analysis;the case where the measurement value of the attached amount was 10 to100 mg/m² was classified as “A,” and the case where the measurementvalue of the attached amount was less than 10 mg/m² or more than 100mg/m² was classified as “B”; the obtained results are collectively shownin Table 5. Note that, for a system containing zirconia, the attachedamount before performing Zr-based FF treatment was measured byfluorescent X-ray analysis in advance, and the value obtained bysubtracting the amount of Zr attached before the chemical conversiontreatment from the amount of Zr attached after the treatment was set asthe attached amount of FF chemical conversion treatment. The method andthe evaluation criterion of the coating adhesiveness evaluation test andthe cycle corrosion test performed on the resulting test material aresimilar to those of the coating adhesiveness evaluation test and thecycle corrosion test performed on the test material on which thephosphate coating film mentioned above was formed. Note that since thepresent invention exhibits satisfactory adhesiveness even in the casewhere the chemical conversion treatability is insufficient, the FFchemical conversion treatability is not a necessary property, and aresult of a system having low FF chemical conversion treatability inwhich the FF chemical conversion treatability is “B”, which is a gist ofthe present invention, is also shown as an index exhibiting satisfactoryadhesiveness.

[Coating Adhesiveness Evaluation Test]

After the phosphate treatment or the FF chemical conversion treatmentdescribed above was performed, the sheet-like hot pressed steel materialof each test number was coated with a cationic electrodeposition coatingmaterial manufactured by Nippon Paint Co., Ltd. by electrodepositionwith slope energization at a voltage of 160 V, and baking coating wasperformed at a baking temperature of 170° C. for 20 minutes. The averageof film thicknesses of the coating material after electrodepositioncoating was 10 μm in all the test numbers.

After the electrodeposition coating, the hot pressed steel material wasdipped in a 5% NaCl aqueous solution having a temperature of 50° C. for500 hours. After the dipping, a polyester tape was adhered to the wholeof an area of 60 mm×120 mm (area A10=60 mm×120 mm=7200 mm²) of the testsurface. After that, the tape was ripped off. The area A2 (mm²) of thecoating film peeled off by the ripping-off of the tape was found, andthe rate of coating peeling (%) was found on the basis of Formula (2).Rate of coating peeling=(A2/A10)×100  (2)

“M” of the “Coating film adhesiveness” section in Tables 3 to 5 meansthat the rate of coating peeling was more than or equal to 50.0%. “L”means that the rate of coating peeling was more than or equal to 35% andless than 50%. “K” means that the rate of coating peeling was more thanor equal to 20% and less than 35%. “J” means that the rate of coatingpeeling was more than or equal to 10% and less than 20%. “I” means thatthe rate of coating peeling was more than or equal to 8% and less than10%. “H” means that the rate of coating peeling was more than or equalto 6% and less than 8%. “G” means that the rate of coating peeling wasmore than or equal to 5% and less than 6%. “F” means that the rate ofcoating peeling was more than or equal to 4% and less than 5%. “E” meansthat the rate of coating peeling was more than or equal to 3% and lessthan 4%. “D” means that the rate of coating peeling was more than orequal to 2.5% and less than 3%. “C” means that the rate of coatingpeeling was more than or equal to 1.3% and less than 2.5%. “B” meansthat the rate of coating peeling was more than or equal to 0.5% and lessthan 1.3%. “A” means that the rate of coating peeling was less than0.5%. The case of “I,” “H,” “G,” “F,” “E,” “D,” “C,” “B,” or “A” in thecoating adhesiveness evaluation was assessed as excellent in coatingadhesiveness.

[Cycle Corrosion Test]

A gap was provided to the coating of the evaluation surface with acutter (load: 500 gf; 1 gf being approximately 9.8×10⁻³ N), and a cyclecorrosion test of the following cycle conditions was performed 180cycles.

Cycle Conditions

A cycle corrosion test was performed in which a procedure of two hoursof salt water spraying (SST; 5% NaCl; atmosphere: 35° C.), then twohours of drying (60° C.), and then four hours of wetting (50° C.; RH:98%) was taken as one cycle.

After that, the presence or absence of a blister of the coating filmoccurring in an area of an approximately 1 cm width from the cut portionwas observed.

“E” of the “Corrosion resistance” section in Tables 3 to 5 means that acoating blister of more than or equal to 3.0 mm occurred. “D” means thata coating blister of more than or equal to 2.0 mm and less than 3.0 mmoccurred. “C” means that a coating blister of more than or equal to 1.0mm and less than 2.0 mm occurred. “B” means that a minute coatingblister of more than or equal to 0.5 mm and less than 1 mm occurred. “A”means that a very minute coating blister of less than 0.5 mm occurred.The case of “C,” “B,” or “A” in the cycle corrosion test was assessed asexcellent in corrosion resistance.

TABLE 3 Zn-based plating Chemical layer conversion Al treatment concen-Surface treatment layer Type of Treat- Corro- tration Attached OxideOxide Oxide chemical ment Coating sion Steel (mass amount A B Cconversion time Treat- adhesiv- resis- No type Type %) Type (g/m²)(g/m²) (g/m²) (g/m²) treatment (sec) ability eness tance Notes 1 #1 GA0.2 1 1 1 0 0 Phosphoric acid 30 J D A 2 #1 GA 0.2 2 1 0.75 0 0Phosphoric acid 30 J D A 3 #1 GA 0.2 3 1 0.4 0 0 Phosphoric acid 30 J DA 4 #1 GA 0.2 4 1 0.2 0 0 Phosphoric acid 30 J G A 5 #1 GA 0.2 5 1 0.5 00 Phosphoric acid 30 J D A 6 #1 GA 0.2 6 1 0.5 0 0 Phosphoric acid 30 JD A 7 #1 GA 0.2 7 1 0.5 0 0 Phosphoric acid 30 J D A Si: 0.006 g/m² 8 #1GA 0.2 8 1 0.5 0 0 Phosphoric acid 30 J D A 9 #1 GA 0.2 9 1 0.5 0 0Phosphoric acid 30 J D A 10 #1 GA 0.2 10 1 0.5 0 0 Phosphoric acid 30 JD A P: 0.029 g/m², Al: 0.008 g/m² 11 #1 GA 0.2 11 1 0.5 0 0 Phosphoricacid 30 J D A Si: 0.047 g/m² 12 #1 GA 0.2 12 1 1 0 0 Phosphoric acid 30J D A 13 #1 GA 0.2 13 1 0.5 0 0 Phosphoric acid 30 J D A 14 #1 GA 0.2 141 1 0 0 Phosphoric acid 30 J J C Comparative Example 15 #1 GA 0.2 15 10.5 0 0 Phosphoric acid 30 J J C Comparative Example 16 #1 GA 0.2 16 10.5 0 0 Phosphoric acid 30 J D C 17 #1 GA 0.2 17 1 0.5 0 0 Phosphoricacid 30 J D C 18 #1 GA 0.2 18 1 0.5 0 0 Phosphoric acid 30 J D C 19 #1GA 0.2 19 1 0.5 0 0 Phosphoric acid 30 J M D Comparative Example 20 #1GA 0.2 20 1 0.5 0 0 Phosphoric acid 30 J D B 21 #1 GA 0.2 21 1 0.5 0 0Phosphoric acid 30 J D B P: 0.029 g/m², Al: 0.008 g/m² 22 #1 GA 0.2 22 10.5 0 0 Phosphoric acid 30 J D B 23 #1 GA 0.2 23 1 0.5 0 0 Phosphoricacid 30 J D B P: 0.029 g/m², Al: 0.008 g/m² 24 #1 GA 0.2 24 1 0.5 0 0Phosphoric acid 30 J D B 25 #1 GA 0.2 25 1 0.5 0 0 Phosphoric acid 30 JD B P: 0.029 g/m², Al: 0.008 g/m² 26 #1 GA 0.2 26 1 0.6 0 0 Phosphoricacid 30 J D B 27 #1 GA 0.2 27 1 0.6 0 0 Phosphoric acid 30 J D B 28 #1GA 0.2 28 1 0.6 0 0 Phosphoric acid 30 J D C 29 #1 GA 0.2 29 1 1 0 0Phosphoric acid 30 M M E Comparative Example 30 #1 GA 0.2 30 1 0.5 0 0Phosphoric acid 30 M M E Comparative Example 31 #1 GA 0.2 31 1 0 0 0Phosphoric acid 30 J M E Comparative Example 32 #1 GA 0.2 32 1 0 0 0Phosphoric acid 30 J M E Comparative Example 33 #2 GA 0.2 5 1 0.5 0 0Phosphoric acid 30 J D A 34 #3 GA 0.2 5 1 0.5 0 0 Phosphoric acid 30 J DA 35 #4 GA 0.2 5 1 0.5 0 0 Phosphoric acid 30 J D A 36 #5 GA 0.2 5 1 0.50 0 Phosphoric acid 30 J D A 37 #6 GA 0.2 5 1 0.5 0 0 Phosphoric acid 30J D A 38 #1 GI 0.4 5 1 0.5 0 0 Phosphoric acid 30 J D A 39 #1 A1 55 5 10.5 0 0 Phosphoric acid 30 J D A 40 #1 A2 6 5 1 0.5 0 0 Phosphoric acid30 J D A 41 #1 A3 11 5 1 0.5 0 0 Phosphoric acid 30 J D A 42 #1 GA 0.2 50.2 0.1 0 0 Phosphoric acid 30 J J D Comparative Example 43 #1 GA 0.2 50.5 0.25 0 0 Phosphoric acid 30 J G C 44 #1 GA 0.2 5 2 1 0 0 Phosphoricacid 30 J D A 45 #1 GA 0.2 5 3 1.5 0 0 Phosphoric acid 30 J D A 46 #1 GA0.2 5 4 2 0 0 Phosphoric acid 30 J G A 47 #1 GA 0.2 5 6 3 0 0 Phosphoricacid 30 J J A Comparative Example 48 #1 GA 0.2 33 2 0.5 0.5 0 Phosphoricacid 30 D A A Si: 0.006 g/m², P: 0.029 g/m², Al: 0.008 g/m² 49 #1 GA 0.234 2 0.5 0.5 0 Phosphoric acid 30 D A A Si: 0.053 g/m² 50 #1 GA 0.2 35 20.5 0.5 0 Phosphoric acid 30 D A A P: 0.029 g/m², Al: 0.008 g/m² 51 #1GA 0.2 36 2 0.5 0.5 0 Phosphoric acid 30 D A A Si: 0.047 g/m² 52 #1 GA0.2 37 2 0.6 0.6 0 Phosphoric acid 30 D A A 53 #1 GA 0.2 38 2 0.6 0.6 0Phosphoric acid 30 D A A 54 #1 GA 0.2 39 2 0.6 0.6 0 Phosphoric acid 30G D B 55 #1 GA 0.2 40 2 0.6 0.6 0 Phosphoric acid 30 G D B 56 #1 GA 0.241 2 0.4 1 0 Phosphoric acid 30 D A A 57 #1 GA 0.2 42 2 0.2 1 0Phosphoric acid 30 D A A 58 #1 GA 0.2 43 2 0.1 0.1 0 Phosphoric acid 30J J C Comparative Example 59 #1 GA 0.2 44 2 0.6 1 0 Phosphoric acid 30 DA A 60 #1 GA 0.2 45 2 0.6 0.6 0 Phosphoric acid 30 D A B 61 #1 GA 0.2 462 0.6 0.6 0 Phosphoric acid 30 D A B 62 #1 GA 0.2 47 2 0.4 0 0.6Phosphoric acid 30 D D A Si: 0.006 g/m², P: 0.029 g/m², Al: 0.008 g/m²63 #1 GA 0.2 48 2 0.4 0 0.6 Phosphoric acid 30 D D A Si: 0.053 g/m² 64#1 GA 0.2 49 2 0.4 0 0.6 Phosphoric acid 30 D D A P: 0.029 g/m², Al:0.008 g/m² 65 #1 GA 0.2 50 2 0.4 0 0.6 Phosphoric acid 30 D D A Si:0.047 g/m² 66 #1 GA 0.2 51 2 0.5 0 0.7 Phosphoric acid 30 D D A 67 #1 GA0.2 52 2 0.5 0 0.7 Phosphoric acid 30 D G C 68 #1 GA 0.2 53 2 0.4 0 0.6Phosphoric acid 30 D G C Si: 0.006 g/m², P: 0.029 g/m², Al: 0.008 g/m²69 #1 GA 0.2 54 2 0.4 0 0.6 Phosphoric acid 30 D G C Si: 0.053 g/m² 70#1 GA 0.2 55 2 0.5 0 0.7 Phosphoric acid 30 D G C 71 #1 GA 0.2 56 2 0.40 0.6 Phosphoric acid 30 D G C Si: 0006 g/m², P: 0.029 g/m², Al: 0.008g/m² 72 #1 GA 0.2 57 2 1 0 0.4 Phosphoric acid 30 D G C 73 #1 GA 0.2 582 0.4 0 0.6 Phosphoric acid 30 D G C Si: 0.006 g/m², P: 0.029 g/m², Al:0.008 g/m² 74 #1 GA 0.2 59 2 0.1 0 0 Phosphoric acid 30 J J C 75 #1 GA0.2 60 2 1 0 0.6 Phosphoric acid 30 D D A 76 #1 GA 0.2 61 3 0.6 0.6 0.9Phosphoric acid 30 A A B 77 #1 GA 0.2 62 3 0.6 0.6 0.9 Phosphoric acid30 A A A 78 #1 GA 0.2 63 3 0.6 0.6 0.9 Phosphoric acid 30 A A B 79 #1 GA0.2 64 3 0.6 0.6 0.9 Phosphoric acid 30 A A B 80 #1 GA 0.2 65 3 0.6 0.60.9 Phosphoric acid 30 A A B 81 #1 GA 0.2 66 3 0.6 0.6 0.9 Phosphoricacid 30 A A A 82 #1 GA 0.2 67 3 0.6 0.6 0.9 Phosphoric acid 30 A A A Si:0.006g/m², P: 0.015 g/m², Al: 0.004 g/m² 83 #1 GA 0.2 68 3 0.6 0.6 0.9Phosphoric acid 30 A A A Si: 0.029 g/m² 84 #1 GA 0.2 69 3 0.6 0.6 0.9Phosphoric acid 30 A A A P: 0.015 g/m², Al: 0.004 g/m² 85 #1 GA 0.2 70 30.6 0.6 0.9 Phosphoric acid 30 A A A Si: 0.023 g/m² 86 #1 GA 0.2 71 30.6 0.6 0.9 Phosphoric acid 30 A A A Si: 0.006 g/m², P: 0.015 g/m², Al:0.004 g/m² 87 #1 GA 0.2 72 3 0.6 0.6 0.9 Phosphoric acid 30 A A A Si:0.029 g/m² 88 #1 GA 0.2 73 3 0.6 0.6 0.9 Phosphoric acid 30 A A A P:0.015 g/m², Al :0.004 g/m² 89 #1 GA 0.2 74 3 0.6 0.6 0.9 Phosphoric acid30 A A A Si: 0.023 g/m² 90 #1 GA 0.2 37 0.5 0.15 0.15 0 Phosphoric acid30 J J D Comparative Example 91 #1 GA 0.2 37 1 0.3 0.3 0 Phosphoric acid30 G D B 92 #1 GA 0.2 37 5 1.0 1.5 0 Phosphoric acid 30 D A A 93 #1 GA0.2 37 6 1.8 1.8 0 Phosphoric acid 30 D A A 94 #1 GA 0.2 51 0.5 0.125 00.175 Phosphoric acid 30 D J D Comparative Example 95 #1 GA 0.2 51 0.250 0.35 Phosphoric acid 30 G G C 96 #1 GA 0.2 51 1 4 0 1.4 Phosphoricacid 30 D A B 97 #1 GA 0.2 51 5 2 0 2.8 Phosphoric acid 30 D A B 98 #2GA 0.2 37 2 0.6 0.6 0 Phosphoric acid 30 D A A 99 #3 GA 0.2 37 2 0.6 0.60 Phosphoric acid 30 D A A 100 #4 GA 0.2 37 2 0.6 0.6 0 Phosphoric acid30 D A A 101 #5 GA 0.2 37 2 0.6 0.6 0 Phosphoric acid 30 D A A 102 #6 GA0.2 37 2 0.6 0.6 0 Phosphoric acid 30 D A A 103 #1 GI 0.4 37 2 0.6 0.6 0Phosphoric acid 30 G D A 104 #1 A1 55 37 2 0.6 0.6 0 Phosphoric acid 30D A A 105 #1 A2 6 37 2 0.6 0.6 0 Phosphoric acid 30 D A A 106 #1 A3 1137 2 0.6 0.6 0 Phosphoric acid 30 G D A 107 #2 GA 0.2 51 2 0.5 0 0.7Phosphoric acid 30 D D B 108 #3 GA 0.2 51 2 0.5 0 0.7 Phosphoric acid 30D D B 109 #4 GA 0.2 51 2 0.5 0 0.7 Phosphoric acid 30 D D B 110 #5 GA0.2 51 2 0.5 0 0.7 Phosphoric acid 30 D D B 111 #6 GA 0.2 51 2 0.5 0 0.7Phosphoric acid 30 D D B 112 #1 GI 0.4 51 2 0.5 0 0.7 Phosphoric acid 30D D B 113 #1 A1 55 51 2 0.5 0 0.7 Phosphoric acid 30 D D B 114 #1 A2 651 2 0.5 0 0.7 Phosphoric acid 30 D D B 115 #1 A3 6 51 2 0.5 0 0.7Phosphoric acid 30 D D B 116 #1 GA 0.2 61 3 0.6 0.6 0.9 Phosphoric acid30 A A A 117 #1 GA 0.2 61 2 0.4 0.4 0.6 Phosphoric acid 30 A A A 118 #1GA 0.2 61 5 1 1 1.5 Phosphoric acid 30 A A A 119 #1 GA 0.2 61 7 1.4 1.42.1 Phosphoric acid 30 A A A 120 #1 GA 0.2 61 9 1.8 1.8 2.7 Phosphoricacid 30 A A A 121 #1 GA 0.2 61 1 0.2 0.2 0.3 Phosphoric acid 30 D D B122 #1 GA 0.2 61 0.5 0.1 0.1 0.15 Phosphoric acid 30 G J C ComparativeExample 123 #4 GA 0.2 61 3 0.6 0.6 0.9 Phosphoric acid 30 A A A 124 #5GA 0.2 61 3 0.6 0.6 0.9 Phosphoric acid 30 A A A 125 #6 GA 0.2 61 3 0.60.6 0.9 Phosphoric acid 30 A A A 126 #7 GA 0.2 61 3 0.6 0.6 0.9Phosphoric acid 30 A A A Mn + Cr 0.4% 127 #8 GA 0.2 61 3 0.6 0.6 0.9Phosphoric acid 30 A A A Mn + Cr 0.6% 128 #1 GI 0.4 61 3 0.6 0.6 0.9Phosphoric acid 30 A A A 129 #1 A1 55 61 3 0.6 0.6 0.9 Phosphoric acid30 A A A 130 #1 A2 6 61 3 0.6 0.6 0.6 Phosphoric acid 30 A A A 131 #1 A311 61 3 0.6 0.6 0.9 Phosphoric acid 30 A A A 132 #1 A4 0 61 3 0.6 0.60.9 Phosphoric acid 30 A A A 133 #1 A5 0 61 3 0.6 0.6 0.9 Phosphoricacid 30 A A A 134 #1 A6 0 61 3 0.6 0.6 0.9 Phosphoric acid 30 A A A 135#1 A4 0 61 3 0.6 0.6 0.9 Phosphoric acid 30 A A A 136 #1 A5 0 61 3 0.60.6 0.9 Phosphoric acid 30 A A A 137 #1 A6 0 61 3 0.6 0.6 0.9 Phosphoricacid 30 A A A 138 #1 GA 0.2 75 2 0.5 0 0.7 Phosphoric acid 30 D D A 139#1 GA 0.2 76 2 0.5 0 0.7 Phosphoric acid 30 D D A 140 #1 GA 0.2 77 3 0.60.6 0.9 Phosphoric acid 30 A A B 141 #1 GA 0.2 78 3 0.6 0.6 0.9Phosphoric acid 30 A A A 142 #1 GA 0.2 79 3 0.6 0.6 0.9 Phosphoric acid30 A A A 143 #1 GA 0.2 80 3 0.6 0.6 0.9 Phosphoric acid 30 A A B 144 #1GA 0.2 81 3 0.6 0.6 0.9 Phosphoric acid 30 A A B 145 #1 GA 0.2 82 3 0.60.6 0.9 Phosphoric acid 30 A A B 146 #1 GA 0.2 5 1 0.5 0 0 Phosphoricacid 10 M G A 147 #1 GA 0.2 83 2 0.6 0.6 0 Phosphoric acid 30 D A A 148#1 GA 0.2 84 2 0.6 0.6 0 Phosphoric acid 30 D A A 149 #1 GA 0.2 85 2 0.60.6 0 Phosphoric acid 30 D A A 150 #1 GA 0.2 86 2 0.6 0.6 0 Phosphoricacid 30 D A B 151 #1 GA 0.2 87 2 0.6 0.6 0 Phosphoric acid 30 D A A 152#1 GA 0.2 88 2 0.6 0.6 0 Phosphoric acid 30 D A A 153 #1 GA 0.2 89 2 0.60.6 0 Phosphoric acid 30 D A A 154 #1 GA 0.2 90 2 0.6 0.6 0 Phosphoricacid 30 D A B 155 #1 GA 0.2 91 2 0.6 0.6 0 Phosphoric acid 30 D A A 156#1 GA 0.2 92 2 0.6 0.6 0 Phosphoric acid 30 D A A 157 #1 GA 0.2 93 2 0.60.6 0 Phosphoric acid 30 D A A 158 #1 GA 0.2 94 2 0.6 0.6 0 Phosphoricacid 30 D A B 159 #1 GA 0.2 95 3 0.6 0.6 0.9 Phosphoric acid 30 A A A160 #1 GA 0.2 96 3 0.6 0.6 0.9 Phosphoric acid 30 A A A

TABLE 4 Zn-based plating layer Chemical Al conversion treatment concen-Surface treatment layer Type of Treat- Corro- tration Attached OxideOxide Oxide chemical ment Coating sion Steel (mass amount A B Cconversion time Treat- adhesiv- resis- No type Type %) Type (g/m²)(g/m²) (g/m²) (g/m²) treatment (sec) ability eness tance Notes 161 #1 GA0.2 5 1.0 0.5 0 0 Phosphoric acid 30 G D A 162 #1 GA 0.2 5 2.0 1.0 0 0Phosphoric acid 30 G D A 163 #1 GA 0.2 5 4.0 2.0 0 0 Phosphoric acid 30G D A 164 #1 GI 0.4 5 2.0 1.0 0 0 Phosphoric acid 30 G D A 165 #1 A1 555 2.0 1.0 0 0 Phosphoric acid 30 G D A 166 #1 A2 6 5 2.0 1.0 0 0Phosphoric acid 30 G D A 167 #1 A3 11 5 2.0 1.0 0 0 Phosphoric acid 30 GD A 168 #1 A4 0 5 2.0 1.0 0 0 Phosphoric acid 30 G D A 169 #1 A5 0 5 2.01.0 0 0 Phosphoric acid 30 G D A 170 #1 A6 0 5 2.0 1.0 0 0 Phosphoricacid 30 G D A 171 #1 GA 0.2 61 1.0 0.5 0 0 Phosphoric acid 30 A A A 172#1 GA 0.2 61 2.0 1.0 0 0 Phosphoric acid 30 A A A 173 #1 GA 0.2 61 4.02.0 0 0 Phosphoric acid 30 A A A 174 #1 GI 0.4 5 2.0 1.0 0 0 Phosphoricacid 30 D A A 175 #1 A1 55 61 2.0 1.0 0 0 Phosphoric acid 30 D A A 176#1 A2 6 61 2.0 1.0 0 0 Phosphoric acid 30 A A A 177 #1 A3 11 61 2.0 1.00 0 Phosphoric acid 30 D A A 178 #1 A4 0 61 2.0 1.0 0 0 Phosphoric acid30 A A A 179 #1 A5 0 61 2.0 1.0 0 0 Phosphoric acid 30 A A A 180 #1 A6 061 2.0 1.0 0 0 Phosphoric acid 30 A A A

TABLE 5 Hot pressing process Zn-based Energization plating layer FFtreatment heating Al Surface treatment coating film Treat- Corro-concen- Attached ment FF Coating sion Steel tration amount Oxide A OxideB Oxide C time treat- adhesiv- resist- No type Type (mass %) Type (g/m²)(g/m²) (g/m²) (g/m² ) Type (sec) ability eness ance Notes 181 #1 GA 0.25 1.0 0.5 0 0 Zr 30 B D A 182 #1 GA 0.2 5 2.0 1.0 0 0 Zr 30 B D A 183 #1GA 0.2 5 4.0 2.0 0 0 Zr 30 B D A 184 #1 GI 0.4 5 4.0 2.0 0 0 Zr 30 B D A185 #1 A1 55 5 2.0 1.0 0 0 Zr 30 B D A 186 #1 A2 6 5 2.0 1.0 0 0 Zr 30 BD A 187 #1 A3 11 5 2.0 1.0 0 0 Zr 30 B D A 188 #1 A4 0 5 2.0 1.0 0 0 Zr30 B D A 189 #1 A5 0 5 2.0 1.0 0 0 Zr 30 B D A 190 #1 A6 0 5 2.0 1.0 0 0Zr 30 B D A 191 #1 GA 0.2 5 1.0 0.5 0 0 Ti 30 B D A 192 #1 GA 0.2 5 2.01.0 0 0 Ti 30 B D A 193 #1 GA 0.2 5 4.0 2.0 0 0 Ti 30 B D A 194 #1 GI0.4 5 4.0 2.0 0 0 Ti 30 B D A 195 #1 A1 55 5 2.0 1.0 0 0 Ti 30 B D A 196#1 A2 6 5 2.0 1.0 0 0 Ti 30 B D A 197 #1 A3 11 5 2.0 1.0 0 0 Ti 30 B D A198 #1 A4 0 5 2.0 1.0 0 0 Ti 30 B D A 199 #1 A5 0 5 2.0 1.0 0 0 Ti 30 BD A 200 #1 A6 0 5 2.0 1.0 0 0 Ti 30 B D A 201 #1 GA 0.2 5 4.0 2.0 0 0 Zr30 A A A 202 #1 GI 0.4 5 4.0 2.0 0 0 Zr 30 A A A 203 #1 A1 55 5 2.0 1.00 0 Zr 30 A A A 204 #1 A2 6 5 2.0 1.0 0 0 Zr 30 A A A 205 #1 A3 11 5 2.01.0 0 0 Zr 30 A A A 206 #1 A4 0 61 3 0.6 0.6 0.9 Zr 30 A A A 207 #1 A5 061 3 0.6 0.6 0.9 Zr 30 A A A 208 #1 A6 0 61 3 0.6 0.6 0.9 Zr 30 A A A209 #1 GA 0.2 5 4.0 2.0 0 0 Ti 30 A A A 210 #1 GI 0.4 5 4.0 2.0 0 0 Ti30 A A A 211 #1 A1 55 5 2.0 1.0 0 0 Ti 30 A A A 212 #1 A2 6 5 2.0 1.0 00 Ti 30 A A A 213 #1 A3 11 5 2.0 1.0 0 0 Ti 30 A A A 214 #1 A4 0 61 30.6 0.6 0.9 Ti 30 A A A 215 #1 A5 0 61 3 0.6 0.6 0.9 Ti 30 A A A 216 #1A6 0 61 3 0.6 0.6 0.9 Ti 30 A A A 217 #1 GA 0.2 5 2.0 1.0 0 0 Zr 10 B GA 218 #1 GA 0.2 5 2.0 1.0 0 0 Ti 10 B G A

TABLE 6 Ion Fluorine Free fluorine Ion Concentration concentrationconcentration source [ppm] [ppm] [ppm] Zr-based FF H₂ZrF₆ 5000 7000 300chemical conversion treatment liquid Ti-based H₂TiF₆ 5000 12000 300 FFchemical conversion treatment liquid

Further, to verify the influence given by a P-containing compound, aV-containing compound, a Cu-containing compound an Al-containingcompound, a Si-containing compound, and a Cr-containing compound presentin the surface treatment layer, plated steel sheets for hot pressingwere produced using the treatment liquids shown in No. 97 to No. 164 ofTable 2. At this time, each of the treatment liquids shown in No. 97 toNo. 164 of Table 2 was applied with a bar coater, and was dried using anoven under conditions for keeping a maximum peak temperature of 100° C.for 8 seconds. The amount of the treatment liquid attached was adjustedby the dilution of the liquid and the count of the bar coater so thatthe total amount of the attached nonvolatile content in the treatmentliquid might be the numerical value shown in Table 7.

After the formation process of the surface treatment layer, the steelsheet of each test number was subjected to hot press heating by anenergization heating system, and thus hot pressing was performed. Atthis time, heating was performed at 870° C., with the heating rate setto 85° C./second and 42.5° C./second.

After the hot press heating, cooling was performed until the temperatureof the steel sheet became 650° C. After the cooling, the steel sheet wassandwiched by a flat sheet mold equipped with a water cooling jacket,and thus a hot pressed steel material (steel sheet) was produced.Cooling was performed up to approximately 360° C., which is themartensite transformation starting point, so as to ensure a cooling rateof 50° C./second or more even in a portion where the cooling rate hadbeen low during the hot pressing, and thus quenching was performed.

The sheet-like hot pressed steel material of each of the test numbersdescribed in Table 7 below was subjected to surface conditioning at roomtemperature for 20 seconds using a surface conditioning treatment agent,Prepalene X (product name) manufactured by Nihon Parkerizing Co., Ltd.Further, phosphate treatment was performed using a zinc phosphatetreatment liquid, Palbond 3020 (product name) manufactured by NihonParkerizing Co., Ltd. The sheet-like hot pressed steel material wasdipped in the treatment liquid for 30 seconds, with the temperature ofthe treatment liquid set to 43° C., and then water washing and dryingwere performed. After that, a phosphate treatability evaluation test wasperformed in a similar manner to the case shown in Table 3.

Further, the sheet-like hot pressed steel material of each of the testnumbers described in Table 7 below was subjected to a coatingadhesiveness evaluation test and a cycle corrosion test in a similarmanner to the case shown in Table 3. The method and the evaluationcriterion of each test are similar to those of the case shown in Table3.

TABLE 7 Zn-based Chemical Hot pressing process plating layer conversiontreatment Energization heating Al Surface treatment layer Type of Treat-Phos- Corro- concen- Attached Oxide Oxide Oxide chemical ment phateCoating sion Steel tration amount A B C conversion time treat- adhesiv-resist- No type Type (mass %) Type (g/m²) (g/m²) (g/m²) (g/m²) treatment(sec) ability eness ance Notes 219 #1 GA 0.2 97 1 0 0 0 Phosphoric acid30 L F A Al: 0.0106 g/m² 220 #1 GA 0.2 98 1 0 0 0 Phosphoric acid 30 K EA Al: 0.0048 g/m² 221 #1 GA 0.2 99 1 0 0 0 Phosphoric acid 30 J D A Al:0.0160 g/m² 222 #1 GA 0.2 100 1 0 0 0 Phosphoric acid 30 L F A Si:0.0093 g/m² 223 #1 GA 0.2 101 1 0 0 0 Phosphoric acid 30 K E A Si:0.0047 g/m² 224 #1 GA 0.2 102 1 0 0 0 Phosphoric acid 30 J D A Si:0.0014 g/m² 225 #1 GA 0.2 103 1 0 0 0 Phosphoric acid 30 J F A P: 0.0107g/m² 226 #1 GA 0.2 104 1 0 0 0 Phosphoric acid 30 J E A P: 0.0043 g/m²227 #1 GA 0.2 105 1 0 0 0 Phosphoric acid 30 J D A P: 0.0011 g/m² 228 #1GA 0.2 106 1 0 0 0 Phosphoric acid 30 J F A V: 0.0148 g/m² 229 #1 GA 0.2107 1 0 0 0 Phosphoric acid 30 J E A V: 0.0074 g/m² 230 #1 GA 0.2 108 10 0 0 Phosphoric acid 30 J D A V: 0.0018 g/m² 231 #1 GA 0.2 109 1 0 0 0Phosphoric acid 30 J F C Cu: 0.0319 g/m² 232 #1 GA 0.2 110 1 0 0 0Phosphoric acid 30 J E B Cu: 0.0160 g/m² 233 #1 GA 0.2 111 1 0 0 0Phosphoric acid 30 J D A Cu: 0.0040 g/m² 234 #1 GA 0.2 112 1 0 0 0Phosphoric acid 30 J D A Cr: 0.0104 g/m² 235 #1 GA 0.2 113 1 0 0 0Phosphoric acid 30 J D A Cr: 0.0042 g/m² 236 #1 GA 0.2 114 2 0 0 0Phosphoric acid 30 F C A Al: 0.0053 g/m² 237 #1 GA 0.2 115 2 0 0 0Phosphoric acid 30 E B A Al: 0.0021 g/m² 238 #1 GA 0.2 116 2 0 0 0Phosphoric acid 30 D A A Al: 0.0005 g/m² 239 #1 GA 0.2 117 2 0 0 0Phosphoric acid 30 F C A Si: 0.0047 g/m² 240 #1 GA 0.2 118 2 0 0 0Phosphoric acid 30 E B A Si: 0.0023 g/m² 241 #1 GA 0.2 119 2 0 0 0Phosphoric acid 30 D A A Si: 0.0005 g/m² 242 #1 GA 0.2 120 2 0 0 0Phosphoric acid 30 D C A P: 0.0128 g/m² 243 #1 GA 0.2 121 2 0 0 0Phosphoric acid 30 D B A P: 0.0043 g/m² 244 #1 GA 0.2 122 2 0 0 0Phosphoric acid 30 D A A P: 0.0009 g/m² 245 #1 GA 0.2 123 2 0 0 0Phosphoric acid 30 D C A V: 0.0074 g/m² 246 #1 GA 0.2 124 2 0 0 0Phosphoric acid 30 D B A V: 0.0037 g/m² 247 #1 GA 0.2 125 2 0 0 0Phosphoric acid 30 D A A V: 0.0007 g/m² 248 #1 GA 0.2 126 2 0 0 0Phosphoric acid 30 D C C Cu: 0.0160 g/m² 249 #1 GA 0.2 127 2 0 0 0Phosphoric acid 30 D B B Cu: 0.0080 g/m² 250 #1 GA 0.2 128 2 0 0 0Phosphoric acid 30 D A A Cu: 0.0016 g/m² 251 #1 GA 0.2 129 2 0 0 0Phosphoric acid 30 D A A Cr: 0.0052 g/m² 252 #1 GA 0.2 130 2 0 0 0Phosphoric acid 30 D A A Cr: 0.0021 g/m² 253 #1 GA 0.2 131 2 0 0 0Phosphoric acid 30 F F A Al: 0.0085 g/m² 254 #1 GA 0.2 132 2 0 0 0Phosphoric acid 30 E E A Al: 0.0042 g/m² 255 #1 GA 0.2 133 2 0 0 0Phosphoric acid 30 D D A Al: 0.0011 g/m² 256 #1 GA 0.2 134 2 0 0 0Phosphoric acid 30 F F A Si: 0.0075 g/m² 257 #1 GA 0.2 135 2 0 0 0Phosphoric acid 30 E E A Si: 0.0037 g/m² 258 #1 GA 0.2 136 2 0 0 0Phosphoric acid 30 D D A Si: 0.0009 g/m² 259 #1 GA 0.2 137 2 0 0 0Phosphoric acid 30 D F A P: 0.0128 g/m² 260 #1 GA 0.2 138 2 0 0 0Phosphoric acid 30 D E A P: 0.0043 g/m² 261 #1 GA 0.2 139 2 0 0 0Phosphoric acid 30 D D A P: 0.0017 g/m² 262 #1 GA 0.2 140 2 0 0 0Phosphoric acid 30 D F A V: 0.0148 g/m² 263 #1 GA 0.2 141 2 0 0 0Phosphoric acid 30 D E A V: 0.0074 g/m² 264 #1 GA 0.2 142 2 0 0 0Phosphoric acid 30 D D A V: 0.0022 g/m² 265 #1 GA 0.2 143 2 0 0 0Phosphoric acid 30 D F C Cu: 0.0319 g/m² 266 #1 GA 0.2 144 2 0 0 0Phosphoric acid 30 D E B Cu: 0.0160 g/m² 267 #1 GA 0.2 145 2 0 0 0Phosphoric acid 30 D D A Cu: 0.0032 g/m² 268 #1 GA 0.2 146 2 0 0 0Phosphoric acid 30 D D A Cr: 0.0156 g/m² 269 #1 GA 0.2 147 2 0 0 0Phosphoric acid 30 D D A Cr: 0.0052 g/m² 270 #1 GA 0.2 148 3 0 0 0Phosphoric acid 30 C C A Al: 0.0111 g/m² 271 #1 GA 0.2 149 3 0 0 0Phosphoric acid 30 B B A Al: 0.0048 g/m² 272 #1 GA 0.2 150 3 0 0 0Phosphoric acid 30 A A A Al: 0.0016 g/m² 273 #1 GA 0.2 151 3 0 0 0Phosphoric acid 30 C C A Si: 0.0084 g/m² 274 #1 GA 0.2 152 3 0 0 0Phosphoric acid 30 B B A Si: 0.0042 g/m² 275 #1 GA 0.2 153 3 0 0 0Phosphoric acid 30 A A A Si : 0.0014 g/m² 276 #1 GA 0.2 154 3 0 0 0Phosphoric acid 30 A C A P: 0.0128 g/m² 277 #1 GA 0.2 155 3 0 0 0Phosphoric acid 30 A B A P: 0.0038 g/m² 278 #1 GA 0.2 156 3 0 0 0Phosphoric acid 30 A A A P: 0.0013 g/m² 279 #1 GA 0.2 157 3 0 0 0Phosphoric acid 30 A C A V: 0.0133 g/m² 280 #1 GA 0.2 158 3 0 0 0Phosphoric acid 30 A B A V: 0.0067 g/m² 281 #1 GA 0.2 159 3 0 0 0Phosphoric acid 30 A A A V: 0.0220 g/m² 282 #1 GA 0.2 160 3 0 0 0Phosphoric acid 30 A C C Cu: 0.0288 g/m² 283 #1 GA 0.2 161 3 0 0 0Phosphoric acid 30 A B B Cu: 0.0144 g/m² 284 #1 GA 0.2 162 3 0 0 0Phosphoric acid 30 A A A Cu: 0.0048 g/m² 285 #1 GA 0.2 163 3 0 0 0Phosphoric acid 30 A A A Cr: 0.0156 g/m² 286 #1 GA 0.2 164 3 0 0 0Phosphoric acid 30 A A A Cr: 0.0078 g/m²

As is clear from Tables 3 to 5 and Table 7 above, it is shown that thezinc-based plated steel sheet according to the present invention hasexcellent coating film adhesiveness after hot pressing even in the casewhere the chemical conversion treatment to be performed thereafter isnot sufficient.

The preferred embodiment(s) of the present invention has/have beendescribed above with reference to the accompanying drawings, whilst thepresent invention is not limited to the above examples. A person skilledin the art may find various alterations and modifications within thescope of the appended claims, and it should be understood that they willnaturally come under the technical scope of the present invention.

The invention claimed is:
 1. A zinc-based plated steel sheet comprising:a zinc-based plated steel sheet that is a base metal; and a surfacetreatment layer formed on at least one surface of the zinc-based platedsteel sheet, wherein the surface treatment layer contains one or moreoxides selected from titanium oxide, and nickel oxide each having aparticle size of more than or equal to 2 nm and less than or equal to100 nm, in a range of more than or equal to 0.2 g/m² and less than orequal to 2 g/m² per one surface, and the surface treatment layer furthercontains one or more vanadium-containing compounds and/or one or morecopper-containing compounds in the following range as a content per onesurface, and contains resin, the one or more vanadium-containingcompounds: more than or equal to 0.0007 g/m² and less than or equal to0.01 g/m² on a V basis, the one or more copper-containing compounds:more than or equal to 0.0016 g/m² and less than or equal to 0.02 g/m² ona Cu basis.
 2. The zinc-based plated steel sheet according to claim 1,wherein the surface treatment layer further contains one or morephosphorus-containing compounds, one or more aluminum-containingcompounds, one or more silicon-containing compounds, and/or one or morechromium-containing compounds in the following range as a content perone surface, the one or more phosphorus-containing compounds: more thanor equal to 0.0 g/m² and less than or equal to 0.01 g/m² on a P basis,the one or more aluminum-containing compounds: more than or equal to 0.0g/m² and less than or equal to 0.005 g/m² on an Al basis, the one ormore silicon-containing compounds: more than or equal to 0.0 g/m² andless than or equal to 0.005 g/m² on a Si basis, and the one or morechromium-containing compounds: more than or equal to 0.0 g/m² and lessthan or equal to 0.01 g/m² on a Cr basis.
 3. The zinc-based plated steelsheet according to claim 1, wherein the particle size of each of the oneor more oxides selected from titanium oxide, and nickel oxide is morethan or equal to 5 nm and less than or equal to 50 nm.
 4. The zinc-basedplated steel sheet according to claim 1, wherein the content of the oneor more oxides selected from titanium oxide, and nickel oxide is morethan or equal to 0.4 g/m² and less than or equal to 1.5 g/m² per onesurface.
 5. The zinc-based plated steel sheet according to claim 1,wherein the one or more oxides are titanium oxide.
 6. The zinc-basedplated steel sheet according to claim 1, wherein the zinc-based platedsteel sheet is a zinc-based plated steel sheet for hot pressing.